Biocu€.a  Lib. 

WW 

100 

V588-- 
1916 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


tc: 


51-13 


Proceedings  of  the  American  Academy  of  Arts  and  Sciences. 
VOL.  51.  No.  13.—  JULY,  1916. 


THE  PATHOLOGICAL  EFFECTS  OF  RADIANT  ENERGY 
ON   THE  EYE 


AX  EXPERIMENTAL  INVESTIGATION 


F.  H-  VERHOEFF,  A.M.,  M.D. 

Pathologist  and  Ophthalmic  Surgeon,  Massachusetts  Charitable  Eye  and  Ear 
Infirmary;    Assistant  Professor  of  Ophthalmic  Research,  Harvard  University. 


Louis  BELL,  PH.D. 

Consulting  Engineer;    Past   President  Illuminating  Engineering   Society. 


WITH  A  SYSTEMATIC  REVIEW  OF  THE  LITERATURE 

BY 

C.  B.  WALKER,  A.M.,  M.D. 

Assistant  in  Ophthalmology,  Harvard  University.      Associate  in  Surgery, 
Bent  Brigham  Hospital. 


FROM  THE   PATHOLOGICAL   LABORATORY   OF  THE  MASSACHUSETTS  CHARITABLE 
EYE   AND  EAR  INFIRMARY. 


(  Couthnifif  from  /»!{/<•  />  of  <-or<  >•.  / 


VOLUME  51. 


1.  THAXTER,  ROLAND. —  New  Indo-Malayan  Laboulbeniales.     pp.  1-51.     August. 

1915      70c. 

2.  URIDQMAN.P.  \V. —  Polymorphic  Transformations  of  Solids  under  Pressure,     pp. 

53-124.     September,  1915.     $1.00. 

3.  WARREN,  CHARLES  H. —  A  Quantitative  Study  of  Certain  Perthitic  Feldspars. 

pp.  125-154      October   1915.     50c. 

•i      DALY.   REGINALD  A. —  The  Glacial-Control  Theory  of  Coral  Reefs,     pp.   155- 
251      November,  1915.     $1.25. 

5.  WHEELER,    WILLIAM    MORTON. —  The    Australian    Honey-Ants    ot    the   Genus 

Leptomyrmex  Mayr.     November,  1915.     pp.  253-286.     50c 

6.  KOFOID,  CHARLES  ATWOOD,  and  SWEZT,  OLIVE. —  Mitosis  and  Multiple  Fission 

in  Trichomonad  Flagellates,     pp.  287-379.     8  pJi.     November,  1915.     $1.50. 

7.  JACKSON,  DUNHAM. —  Expansion  Problems  with  Irregular  Boundary  Conditions. 

pp.  381-417.     November,  1915.     70c. 

8.  KENNELLY,  A.  E.,  and  AFFEL,  H.  A. —  The  Mechanics  of  Telephone- Receiver 

Diaphragms,  as  Derived  from  their  Motional-Impedance  Circles,  pp.  419- 
482.  November,  1915.  $1.25. 

9      MAVOR,  J.  W. —  On  the  Development  of  the  Coral  Agaricia  fragilis  Dana.     pp. 
483-511.     6  pll.     December,  1915.     90c. 

10.  BLAKE,  S.   F. —  (I)    Compositae  new   and   transferred,  chiefly  Mexican;     (II) 

ROBINSON,  B.  L. —  New,  reclassifled,  or  otherwise  noteworthy  Spermato- 
phytes;  (III)  MACBRIDE,  J.  FRANCIS. —  Certain  Borraginaceae  new  or  trans- 
ferred, pp.  513-548.  January,  1916.  50c. 

11.  MAYOR,  JAMES  W. —  On  the  Life-History  of  Ceratomyxa  acadiensis,  a  new 

species  of  Myxosporidia  from  the  eastern  coast  of  Canada,    pp.  549-578. 

3  pll.     April,  1916.     70c. 
12      BRIDGMAN,  P.  W. —  Polymorphic  Changes  under    Pressure  of  the  Univalent 

Nitrates,     pp.  579-625.     April,  1916      70c. 
1:5.      VERHOEFF,  F.  H.,  BELL,  Louis,  and  WALKER,  C.  B. — The  Pathological   Effects 

of  Radiant  Energy  upon  the  Eye.    pp.  027-818.    (8  pis.)    July,  19U5.    $1.50. 


Proceedings  of  the  American  Academy  of  Arts  and  Sciences. 

VOL.  51.  Xo.  13.  — JULY,  1916. 


THE  PATHOLOGICAL  EFFECTS  OF  RADIANT  ENERGY 
ON   THE  EYE 


AX  EXPERIMENTAL  INVESTIGATION 

BY 

F.  H.  VERHOEFF,  A.M.,  M.D. 

Pathologist  and  Ophthalmic  Surgeon,  Massachusetts  Charitable  Eye  and  Ear 
Infirmary;    Assistant  Professor  of  Ophthalmic  Research,  Harvard  University. 

AND 

Louis  BELL,  PH.D. 

Consulting  Engineer;    Past  President  Illuminating  Engineering   Society. 


WITH  A  SYSTEMATIC  REVIEW  OF  THE  LITERATURE 
/ 

BY 

C.  B.  WALKER,  A.M.,  M.D. 

Assistant  in  Ophthalmology,  Harvard  University.     Associate  in  Surgery, 
Peter  Bent  Brigham  Hospital. 


FROM  THE   PATHOLOGICAL  LABORATORY   OF  THE  MASSACHUSETTS  CHARITABLE 
EYE   AND  EAR  INFIRMARY. 


INM  STK.ATION-.    UN     LlUHT    AND    HfrlAT     MADE     AND     PUBLISHED     WITH     AID     PROM     THE 

RUMFORD    FUND. 


Biomsdical 
ay 

WIO 
ICO 


Ififc 

THE    PATHOLOGICAL   EFFECTS   OF    RADIANT   ENERGY 
UPON  THE  EYE. 

TABLE  OF  CONTENTS. 

PAGE 

Introduction     ....................  630 

Photophthalmia    ...................  634 

Determination  of  Liminal  Exposure     ..........  638 

Verification  of  Law  of  inverse  squares      ...     ......  640 

Effect  of  Repeated  Exposures      ............  641 

Limit  of  Abiotic  Action  with  respect  to  Wave  Length     .....  645 

Record  of  Experiments  (Nos.  37  to  93)     .......  -  .     .  652 

Histological  Technique    ...............  660 

Reactions  of  Ocular  Tissues  to  Abiotic  Radiation   .......  662 

Clinical;  Conjunctiva  and  Cornea    ...........  662 

Histological  Changes  Found       ..............  665 

Cornea      ....................  665 

Conjunctiva       ..................  669 

Iris        ........     :     ............  670 

Lens      .....................  671 

Possible  Abiotic  Effects  on  Retina     ............  677 

Experiments  on  Eyes  of  Rabbits  ............  679 

Experiments  on  Eyes  of  Monkeys        ..........  681 

Experiment  on  Human  Eye    .............  684 

Possible  Abiotic  Effects  on  retina  of  Aphakic  Eye    ......  686 

Refutation  of  Birch-Hirschfeld's  Findings        .........  687 

Thermic  Effects  of  Radiant  Energy   ............  692 

Cornea      ....................  692 

Iris  and  Lens    ..................  696 

Retina       ....................  '  697 

Record  of  Experiments  with  concentrated  sunlight  (Nos.  95  to  101)     .  699 

Theory  of  Action  of  Radiant  Energy  on  the  Tissues    .......  703 

Abiotic  Energy  in  the  Solar  Spectrum    ............  705 

Snow  Blindness      .................  706 

Solar  Erythema      .................  708 

Erythropsia        ..................  710 

Vernal  Catarrh       .................  713 

Senile  cataract        ............     .....  715 

Concentration  of  Energy  in  Images             ..........  716 

General  Nature  of  Absorption  of  Radiant  Energy    ........  717 

Eclipse  Blindness  and  Allied  Phenomena    ..........  720 

Possible  Specific  Action  of  Infra-Red      ...........  728 

Experiment  relating  to  accuracy  of  fixation    ........  732 

Glass  Blowers'  Cataract      ..............  734 

Applications  to  Commercial  Illuminants      ..........  737 

Experiment  with  nitrogen  lamp   ............  738 

Experiment  with  quartz  mercury  lamp  enclosed  in  globe     .     .     .  742 

Protective  Glasses    ..................  744 

Ultra  Violet  Light  as  a  Germicidal  Agent.     Experimental 

Investigation  of  its  Possible  Therapeutic  Value     ......  749 

General  Conclusions      .................  756 

Systematic  Review  of  the  Literature  —  C.  B.  Walker      .....  760 

Bibliography    ...............          ....  794 

Plates      ..................  811 


590566 

Af  *  d  i  a   »j  «    • 


^630  VERHOEFF  AND   BELL. 

THE  fundamental  purpose  of  this  investigation  has  been  to  dis- 
cover what  if  any  pathological  effects  can  be  produced  upon  the 
structure  of  the  eye  by  exposure  to  artificial  or  natural  sources  of 
light.  That  such  action  may  occur  under  sufficiently  powerful 
exposure  to  radiant  energy  is  certain,  but  the  essential  fact  is  the 
discovery  of  the  quantitative  relations  between  the  amount  of  incident 
energy  and  the  effects.  These  relations  have  generally  been  left 
quite  out  of  the  reckoning  in  discussing  the  subject,  with  the  result 
of  leading  to  vague  and  often  quite  unwarranted  conclusions  as 
irrelevant  as  if  one  should  condemn  steam  heating  as  dangerous 
because  one  can  burn  his  finger  upon  a  radiator. 

The  quantitative  phase  of  the  matter  is,  from  a  practical  standpoint, . 
all-important  since  on  it  depends  the  actual  effects  to  be  expected 
from  the  exposure  of  the  eye  to  powerful  natural  or  artificial  sources 
of  light.  Although  the  literature  of  the  subject  is  very  extensive, 
the  appended  bibliography  covering  over  450  titles,  practically  none 
of  the  work  done  has  been  quantitative  in  the  sense  of  connecting 
the  amount  and  kind  of  the  energy  received  with  the  effects  produced, 
and  hence,  despite  the  work  of  many  careful  investigators,  the  results 
have  been  singularly  discordant  and  inconclusive,  so  that  a  coordi- 
nation of  the  facts  from  the  standpoint  of  energy  has  seemed  impera- 
tive. One  of  us  19  has  investigated  recently  the  energy  relations 
of  the  radiation  from  various  sources  of  light  both  natural  and  arti- 
ficial, and  the  intent  of  the  present  investigation  has  been  to  determine 
by  actual  experiment  on  the  eye  the  quantitative  and  qualitative 
effects  of  radiant  energy  on  the  conjunctiva,  cornea,  iris,  lens,  and 
retina. 

It  has  long  been  known  that  excessive  radiation  of  one  kind  or 
another  produces  pathological  changes  in  the  eye,  of  many  kinds  and 
greatly  varying  degrees  of  intensity.  So  far  as  natural  light  is  con- 
cerned the  well  known  effects  of  powerful  solar  radiation  in  producing 
snow  blindness  and  allied  troubles  have  been  long  familiar  as  also 
have  been  the  severe  scotomata  due  to  direct  observation  of  the  sun, 
familiar  in  the  literature  under  the  general  name  of  eclipse  blindness. 
With  the  introduction  of  the  electric  arc,  mild  cases  of  ocular  trouble 
due  to  over  exposure  to  the  arc  began  to  attract  attention,  at  first 
nearly  a  half  a  century  ago,  and  the  subject  has  occupied  an  increasing 
space  in  the  literature  ever  since.  More  recently  attention  has  been 
particularly  drawn  to  the  ultra  violet  radiation  as  productive  of  these 
pathological  conditions,  and  most  of  the  investigations  bearing  on  the 
.general  subject  have  been  directed  toward  the  study  of  the  specific 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         631 

action  of  the  ultra  violet.  It,  therefore,  becomes  of  fundamental 
importance  to  examine  the  effects  of  radiant  energy  with  special  refer- 
ence to  their  relation  to  the  wave  length  of  the  radiation. 


NATURE  AND  DISTRIBUTION  OF  RADIANT  ENERGY. 

All  radiant  energy  is  at  present  believed  to  consist  of  transverse 
vibrations  in  the  hypothetical  ether,  all  propagated  at  the  same  rate 
and  differing  only  in  amplitude  and  wave  length,  hence  in  frequency, 
which  is  the  reciprocal  of  wave  length.  The  uniform  propagation 
rate  in  vacuo  is  very  nearly  300,000  km.  per  second  and  the  wave 
lengths  so  far  as  ordinarily  dealt  with  range  from  about  .01  to  about 
.0002  mm.  For  ordinary  purposes  no  attention  need  be  paid  to  the 
extremely  long  wave  lengths  ranging  to  .1  mm.,  to  the  extremely 
short  ones  between  .0001  and  .0002  mm.,  or  to  the  enormously  shorter 
one  still  of  the  order  of  magnitude  of  .0000001  mm.  such  as  the  X-rays 
are  believed  to  be.  For  the  very  long  waves  are  not  present  in  material 
amount  in  the  radiation  from  ordinary  sources.  The  very  short  ones 
are  absorbed  by  a  few  cm.  or  dm.  of  air,  and  the  X-rays  are  practically 
only  produced  in  apparatus  intended  for  that  purpose.  The  spectra 
given  by  all  ordinary  sources  range  between  the  more  modest  limits 
just  given.  In  the  earlier  literature  this  spectral  range  used  to  be 
divided  into  heat  rays,  light  rays,  and  actinic  rays,  a  distinction 
wholly  artificial  since  the  three  effects  implied  are  far  from  being 
sharply  defined.  More  generally  the  whole  range  is  divided  into  the 
infra  red  portion,  not  ordinarily  visible  and  extending  from  the  longest 
waves  to  thqse  of  about  760  MM>  the  visible  spectrum,  extending  from 
about  760  MM  to  about  395  MM>  and  the  ultra  violet  portion  reaching 
from  395  MM  to'  the  neighborhood  of  200  MM-  This  distinction  is  not 
rigorous  or  with  sharp  limits.  While  artificial  distinctions  have  led 
to  many  misunderstandings,  all  radiation  of  whatever  wave  length 
is  convertible  into  heat  when  absorbed  by  material  bodies  and  may 
produce  chemical  changes  as  well.  As  a  matter  of  fact  these  latter 
show  a  general  tendency  to  increase  with  the  frequency  of  the  oscilla- 
tions, so  that  chemical  changes  are  rare  in  the  infra  red  and  increasingly 
frequent  as  one  approaches  the  extreme  ultra  violet.  It  is  this  tend- 
ency that  is  shown  in  the  pathological  changes  which  may  be  caused 
in  living  cells  by  the  incidence  of  radiation. 

The  rationale  of  the  chemical  effect  of  radiation  seems  to  be  that 
while  all  radiation  transfers  energy  to  the  molecules  which  absorb  it 


632  VERHOEFF  AND   BELL. 

and  produce  heat,  certain  particular  wave  frequencies  fall  into  step, 
as  it  were,  with  the  oscillation  periods  which  depend  on  the  mo- 
lecular structure,  and  so  break  up  the  molecules  when  the  energy 
absorbed  is  sufficient.  The  particular  kind  of  radiation  which  pro- 
duces this  direct  action  depends  on  the  character  of  the  molecules. 
Thus,  for  instance,  the  green  modification  of  silver  bromide  is  readily 
broken  up  by  radiation  of  wave  length  as  great  as  1  /z,  while  it  requires 
radiation  of  double  this  frequency  to  affect  or.dinary  silver  bromide, 
and  the  molecules  of  living  protoplasm  begin  to  break  up  only  when 
the  wave  length  is  down  to  about  300  /J./JL  as  we  shall  show.  But  most 
chemical  compounds  are  unaffected  by  any  practical  amount  of 
radiation  which  may  fall  upon  them  except  as  they  may  be  heated  to 
the  point  of  decomposition.  Any  effect  which  is  due  to  radiation 
is  in  the  last  analysis  dependent  on  the  absorption  of  that  radiation, 
in  that  there  is  involved  a  transfer  of  energy  to  the  molecules  or  their 
parts  in  order  that  they  may  be  heated  or  shaken  apart.  Every  sub- 
stance absorbs  radiant  energy  in  greater  or  less  degree,  and  the  amount 
of  absorption  bears  a  definite  relation  to  the  thickness  of  the  body  as 
well  as  to  the  particular  wave  length  of  the  incident  energy.  Certain 
substances,  like  fluorite  and  to  a  less  degree  quartz,  let  pass  with  very 
little  obstruction  radiation  from  far  into  the  infra  red  to  wave  length 
200  H/JL.  Water  absorbs  the  longer  wave  lengths  of  the  infra  red  up 
to  about  1.2  n  powerfully,  and  transmits  nearly  everything  else  up  to 
the  extreme  ultra-violet,  while  pure  air,  generally  speaking  extremely 
transparent,  produces  some  small  but  sharp  absorption  in  the  visible 
spectrum  and  completely  wipes  out  the  extreme  ultra  violet.  But 
whatever  the  wave  length,  the  law  connecting  the  absorption  of  energy 
with  thickness  of  the  medium  is  extremely  definite.  If  a  layer  of  unit 
thickness  transmits  a  certain  fraction  T  then  any  other  thickness  x  will 
transmit  a  fraction  Tx  of  the  incident  energy.  Thus,  if  a  substance 
transmits  badly,  leading  to  a  low  value  of  T,  very  little  energy  gets 
through  the  outermost  layers,  while  if  it  be  fairly  transparent  a  con- 
siderable amount  of  energy  penetrates  deeply.  For  example,  a  cer- 
tain Jena  glass  transmits  violet  light  through  1  mm.  of  thickness 
with  only  a  small  fractional  per  cent  of  loss.  It  transmits  the  same 
ilight  through  a  cm.  of  thickness  with  the  loss  of  only  2%,  while 
mear  the  extreme  ultra  violet  of  the  solar  spectrum  it  still  transmits 
a  little  over  90%  for  a  mm.  of  thickness,  but  barely  38%  through  a  cm. 
Where,  therefore,  radiant  energy  falls  on  a  solid  upon  which  through 
absorption  it  produces  powerful  chemical  action,  the  immediate  effect 
will  be  almost  wholly  superficial,  and  only  by  prolonged  and  intense 


EFFECTS    OF    RADIANT    ENERGY   ON   THE    EYE. 


633 


radiation  can  enough  energy  be  communicated  into  interior  layers  to 
affect  them  in  a  similar  manner.  To  put  the  thing  in  another  way,  it  is 
only  relatively  inactive  rays  that  through  consequent  lack  of  absorp- 
tion penetrate  a  medium  easily.  With  sufficient  incident  intensity, 
however,  enough  energy  may  penetrate  the  outer  layers  to  produce 
definite  action  within  them. 

In  ordinary  transparent  media  the  loss  of  energy  by  real  absorption 
in  the  substance  is  less  than  the  loss  at  the  surfaces  by  reflection. 
This  loss  depends  on  the  refractive  index  of  the  medium  with  respect 
to  the  entering  or  emerging  ray,  and  for  nearly  normal  incidence  the 
coefficient  of  reflection,  that  is  the  proportion  of  the  ray  transmitted 


through  a  single  reflecting  surface  is  K  = 


This  coefficient 


(n+1)' 

is  the  same  for  each  successive  surface  of  transition,  so  that  for  m 
surfaces  the  coefficient  of  transmission  are  Km  =  Km.  Thus,  if 
a  glass  plate  has  an  index  of  refraction  n  the  light  transmitted  is  K2 


9 
8 
7 
6 
6 
4 
3 
2 
I 
90 
9 
8 
7 
1 
5 
4 
3 
2 
1 
Ml 

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=^ 

^s 

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X 

X 

™ 

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X 

\ 

X 

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, 

V 

\ 

\ 

\ 

X 

\ 

a^ 

S 

> 

\ 

\ 

s 

\ 

\ 

b 

1.0     1.1      1.2      1.3      1.4      l.i      1.6       1.7      1.8 


FIGURE  1.    Transmission  of  glass  surfaces. 

for  the  two  surfaces.  In  case  of  an  optical  system  having  several 
lenses,  the  reflection  losses  may  be  severe,  particularly  if  some  of  the 
glasses  are  of  high  index.  Figure  1  shows  in  curve  a  the  transmission 
of  a  single  surface  for  various  indices  of  refraction,  and  in  curve  b 
transmission  of  a  double  surface  like  that  presented  by  a  transparent 


634 


VERHOEFF  AND   BELL. 


plate.  The  reflection  is  a  function  as  well  of  the  angle  of  incidence, 
but  for  the  ordinary  angles  up  to  30  degrees  or  so  the  variation  is 
negligible.  At  large  angles  of  incidence  such  as  would  be  presented, 
for  instance,  by  the  marginal  rays  of  a  beam  incident  upon  the  cornea 
the  loss  by  reflection  may  be  considerably  more  than  doubled  so  as  to 
materially  reduce  the  amount  of  energy  absorbed. 

In  any  case  the  surface  density  of  the  energy  received  by  the  cornea 


'•5      40 


\ 


012345        G  ui.iii. 

Distance  from  axis 
FIGTJBB  2.     Distribution  of  radiant  energy  on  cornea. 

under  such  circumstances  is  diminished,  following  Lambert's  law,  in 
direct  proportion  to  the  cosine  of  the  angle  of  incidence.  The  net 
result  is  that  from  parallel  rays  the  cornea  receives  a  much  greater 
incidence  of  energy  per  unit  area  in  the  centre  than  toward  the  margin, 
which  accounts  for  some  of  the  results  to  be  recorded  later.  Figure  2 
shows  for  the  average  rabbit's  cornea  the  approximate  variation  in  the 
intensity  of  energy  per  unit  area  from  centre  to  periphery. 


PHOTOPHTHALMIA. 


Inasmuch  as  most  of  the  pathological  changes  in  the  eye  observed, 
after  exposure  to  light,  either  clinically  or  experimentally,  have  been 
ascribed  to  the  action  of  the  ultra  violet  part  of  the  spectrum,  it  is 
with  this  that  our  work  has  chiefly  been  done,  although  we  have  also 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          635 

examined  the  effect  of  the  other  radiations  which  are  received  from 
natural  or  artificial  sources. 

Our  first  aim  was  to  ascertain  what  quantitative  relations  existed 
.  between  the  incidence  of  energy  on  the  eye  and  the  pathological  effects 
which  might  follow.  Especially  we  desired  to  ascertain  whether 
these  effects  were  proportional  to  the  incident  energy  and  hence  to 
such  primary  lesions  as  might  be  produced  by  it,  or  serve  to  set  in 
train  pathological  changes  of  an  extent  not  proportionate  to  the 
primary  inducing  cause.  To  this  end  we  first  turned  our  attention 
to  the  so-called  ophthalmia  electrica  or  photophthalmia  (Parsons), 
at  once  the  earliest  known  and  commonest  of  the  superficial  pathologi- 
cal effects  of  radiation.  Probably  first  observed  by  Foucault  and 
Despretz  about  sixty  years  ago,  it  received  its  first  notice  from  the  medi- 
cal standpoint  in  a  paper  by  Dr.  Charcot.66  His  brief  clinical  observa- 
tions are  here  reproduced  in  full  as  they  are  typical  so  far  as  the 
external  effects  go  of  a  mild  case  of  this  particular  affection.  The 
luminous  effects  as  described,  are  not  characteristic  and  were  no 
doubt  purely  psychical,  and  due  perhaps  to  undue  attention  having 
been  called  to  the  sensations  of  light  normally  arising  in  the  dark 
adapted  eye.  The  fusion  and  vitrification  of  refractory  substances 
produce  far  more  intense  effects  of  .this  kind  than  would  have  been 
noted  in  the  other  experiments  cited  by  Dr.  Charcot. 

ERYTHEMA  PRODUCED  BY  THE  ACTION  OF  THE  ELECTRIC  LIGHT.  BY  DR. 
CHARCOT. —  The  fourteenth  of  February  last  two  chemists  were  cooperating  in 
making  some  experiments  on  the  fusion  and  vitrification  of  certain  substances 
by  the  action  of  the  electric  battery.  They  made  use  of  a  Bunsen  battery  of 
120  elements.  The  experiments  lasted  about  an  hour  and  a  half;  but  during 
this  time  the  action  of  the  battery  was  frequently  interrupted  and  it  was  not 
working  in  all  more  than  twenty  minutes.  At  the  distance  of  the  experi- 
menters from  the  arc,  about  fifty  cm.,  they  were  not  sensible  of  a  rise  in  tem- 
perature. Nevertheless,  that  evening  and  during  the  whole  night  which  they 
passed  without  sleep  they  found  in  their  eyes  a  feeling  of  severe  irritation  and 
saw  almost  continually  flashes  and  colored  spots.  The  next  day  both  had 
upon  their  faces  erythema  of  a  purplish  color  with  a  feeling  of  pain  and  tension. 
In  the  case  of  M.  W.,  the  right  side  of  whose  face  alone  was  exposed  to  the 
luminous  arc,  the  reddening  covered  that  whole  side  from  the  roots  of  the  hair 
to  the  chin,  and  the  sparks  were  only  seen  as  if  before  his  right  eye.  In  the 
case  of  M.  M.  who  had  held  his  head  lower  and  whose  face  had  been  protected 
against  the  arc  by  his  brow,  the  brow  only  was  affected  with  erythema.  Upon 
both  the  experimenters  the  appearance  of  the  skin  in  the  parts  affected  was 
exactly  that  of  sunburn;  a  slight  desquamation  was  established  at  the  end  of 
four  days  and  lasted  in  all  five  or  six  days. 


636  VERHOEFF  AND   BELL. 

This  effect  of  the  electric  light  is  very  curious  and  in  its  pathology  one  may 
perhaps  find  the  rationale  of  sunburn  properly  so-called.  Everybody  knows  a 
high  temperature  is  not  a  necessary  condition  for  the  production  of  this  last 
affection,  for  there  are  some  people  who  are  attacked  in  the  cool  weather  of  the 
first  days  of  spring,  a  fact  analogous  to  those  which  we  here  report.  Both  • 
concur  in  showing  that  in  the  radiation  of  the  light  it  is  not  the  calorific  rays 
which  attack  the  skin. 

Must  one  then  invoke  the  action  of  the  luminous  rays  themselves?  No,  or 
at  least  the  intensity  of  the  light  seems  to  play  only  a  secondary  role.  Indeed 
in  the  experiments  made  by  M.  Foucault  in  coupling  several  Ruhmkorff  coils 
to  produce  sparks  of  which  the  length  increased  with  the  number  of  bobbins 
and  where  he  had  been  able  by  the  means  of  a  double  action  interrupter  to 
double  the  number  of  these  sparks  without  diminishing  their  energy,  this 
observer  was  attacked  by  headache,  very  marked  and  persistent  troubles  of 
vision  and  erythema,  although  the  light  was  not  more  intense  than  that  of  a 
star  which  one  looks  at  without  fatigue.  M.  Despretz  has  noted  that  light 
obtained  with  100  Bunsen  elements  produces  eyeache  and  that  from  600  ele- 
ments very  rapidly  produces  erythema. 

There  remain  the  so-called  chemical  rays  and  it  is  this  sort  of  rays  which 
seems  to  be  the  principle  essential  agent  of  the  accidents.  To  protect  the  eyes, 
it  suffices  as  M.  Foucault  has  several  times  noted,  to  let  the  electric  light  pass 
through  a  uranium  glass  screen  which  absorbs  a  large  proportion  of  the  chemi- 
cal rays.  Doubtless  by  protecting  the  face  with  this  same  uranium  glass  one 
would  avoid  also  the  production  of  erythema.  The  very  rapid  and  energetic 
action  of  the  electric  light  upon  the  skin  and  upon  th6  retina  one  can  under- 
stand the  better  since  the  chemical  rays  in  it  are  as  is  well  known  relatively 
more  abundant  than  in  the  solar  light. 

An  ordinary  clinical  case  of  photophthalmia  as  observed  after 
exposure  to  arc  lights,  short  circuits,  and  the  like,  commonly  takes 
the  following  course.  After  a  period  of  latency,  varying  somewhat 
inversely  with  the  severity  of  the  exposure,  but  usually  several  hours, 
conjunctivitis  sets  in  accompanied  by  erythema  of  the  surrounding 
skin  of  the  face  and  eyelid.  There  is  the  sensation  of  foreign  body 
irritation,  more  or  less  photophobia,  lacrimation,  and  the  other  ordi- 
nary symptoms  of  slight  conjunctivitis.  Occasionally  there  is  some 
chemosis.  The  symptoms  usually  pass  off  in  two  or  three  days,  and  in 
severe  cases  there  may  be  desquamation  of  the  affected  epidermis 
around  the  eye.  In  a  very  few  instances  the  cornea  has  been  slightly 
and  temporarily  affected.  There  is  almost  always  immediately  fol- 
lowing the  exposure,  and  quite  unconnected  with  the  photophthalmia 
proper,  the  ordinary  results  of  a  glare  of  light  in  the  eyes,  persistent 
after  images,  occasional  scotomata,  erythropsia  and  xanthopsia. 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          G37 

The  diagnosis  and  prognosis  we  can  hardly  better  state  than  in  the 
words  of  Van  Lint  381  in  his  report  to  the  Belgian  Ophthalmological 
Society. 

"  Diagnosis :  The  symptoms  and  evolution  of  the  malady  character- 
ize very  clearly  accidents  provoked  by  electric  light.  Nevertheless, 
the  diagnosis  is  sometimes  delicate.  Certain  people,  especially 
employees  working  habitually  by  electric  light,  complain  of  ocular 
troubles  which  they  assign  to  the  influence  of  electricity.  These 
troubles  have  for  the  most  part  no  relation  to  the  cause  invoked. 
In  the  patient  affected  by  conjunctivitis  one  generally  finds  a  slight 
infective  conjunctivitis,  if  by  troubles  of  vision  one  finds  asthenopia 
due  either  to  a  local  cause,  hypermetropia  or  astigmatism,  or  to  a 
general  cause  anemia,  fatigue  or  the  like.  One  must  consequently 
eliminate  all  these  outside  causes  before  concluding  that  the  troubles 
are  chargeable  to  the  electric  light." 

"Prognosis:  As  one  is  able  to  see  after  a  study  of  the  symptoms 
the  prognosis  is  always  favorable.  A  duration  of  about  five  days 
seems  to  be  necessary  for  the  course  of  the  malady.  In  case  of  nervous 
asthenopia  the  prognosis  is  equally  favorable  provided  one  protects 
the  patient  against  the  luminous  sources.  A  case  cited  by  Fere 
endured  six  weeks,  but  the  patient  was  affected  by  nervous  symptoms 
which  had  very  remote  relation  with  those  provoked  by  electric  light." 

Our  first  series  of  experiments  was  concerned  with  the  relation 
between  cause  and  effect  in  photophthalmia  of  rabbits  following 
exposure  to  a  powerful  source  of  ultra  violet  radiation.  As  the  source 
of  energy  we  employed  a  quartz  mercury  lamp  operating  on  220  volt 
circuit  and  normally  taking  3.5  amperes  with  about  90  volts  across 
the  terminals  of  the  tube.  This  was  the  same  lamp  of  which  the  radia- 
tion has  already  been  studied  by  one  of  us 19  and  which  furnishes 
by  far  the  best  source  of  energy  for  such  experiments,  inasmuch  as  its 
ultra  violet  radiation  is  powerful  and  the  light  after  running  twenty  to 
thirty  minutes  to  heat  up  is  extraordinarily  steady.  It  is  also  remark- 
ably advantageous  in  the  distribution  of  energy  in  its  spectrum,  since 
it  gives  off  relatively  little  radiation  of  long  wave  length,  the  nearer 
infra  red  region  being  particularly  weak,  so  that  results  obtained  by 
it  are  not  complicated,  save  in  some  experiments  with  bacteria,  by 
any  effects  due  purely  to  temperature.  Although  there  is  consider- 
able heat  loss  in  the  lamp  it  is  nearly  all  in  the  form  of  heat  waves  of 
very  long  wave  length  which  are  wholly  cut  off  by  a  cell  containing 
pure  water,  the  infra  red  lines  of  the  spectrum  being  very  few.  As 
respects  the  radiation  from  this  lamp,  therefore,  it  is  practically  all 


638  VERHOEFF  AND   BELL. 

in  the  visible  and  ultra  violet  portions  of  the  spectrum,  35%  being  in 
the  visible  spectrum  itself  and  65%  in  the  ultra  violet  between  wave 
lengths  400ju/x  and  200/i/z.  This  65%  is  equally  divided  between 
wave  lengths  400  yuju  to  300  /x/x  and  300  juju  to  200  (JL/JL,  as  one  of  us 
has  already  shown  (loc.  cit.).  As  the  lamp  was  run  the  total  radia- 
tion of  energy  having  wave  lengths  less  than  400  /JL/J,  at  a  distance  of 
50  cm.  from  the  tube  was  to  a  very  close  approximation  11,000  ergs 
per  second  per  square  cm.,  of  which  5,500  ergs  per  square  cm.  of 
energy  were  of  wave  length  less  than  300  /J./JL.  At  distances  other  than 
the  standard  one  here  noted,  the  radiation  follows  the  law  of  inverse 
squares  with  substantial  precision.  A  small  correction  should  theo- 
retically be  applied  because  the  radiating  body  is  approximately  a 
cylinder  instead  of  a  point.  But  for  all  practical  purposes  this 
correction  may  be  neglected,  since  for  a  radiative  body  of  the  dimen- 
sions used  it  amounts  to  less  than  one  quarter  of  1%  at  all  distances 
greater  than  50  cm.,  and  does  not  exceed  2%  even  when  the  distance  is 
reduced  to  20  cm.  Plate  5,  Fig.  1,  shows  the  actual  spectrum  of  the 
quartz  lamp  taken  with  a  rather  wide  slit  and  prolonged  exposure  with 
wave  length  scale  annexed,  and  Figure  2  shows  the  stronger  lines  of 
the  visible  spectrum  alone.  The  lines  toward  the  right  of  A,  which 
do  not  appear  in  B,  are  merely  the  ultra  violet  lines  of  the  over- 
lapping second  order  spectrum,  the  photograph  having  been  taken 
with  a  concave  grating  of  1  meter  focal  length  and  10,000  lines  to  the 
inch.  Attention  should  be  called  to  one  interesting  feature  of  this 
mercury  arc  spectrum.  It  will  be  seen  that  there  is  but  a  single  ultra 
violet  line  between  the  strong  double  line  at  313  /z/z  and  the  strong 
group  at  365  up  and  this  line  is  relatively  weak.  There  is  also  a, 
conspicuous  gap  between  313  and  the  next  line  at  approximately 
303  nn.  These  gaps  in  the  spectrum  are  of  some  significance  in  inter- 
preting bactericidal  experiments  in  this  region  of  the  spectrum. 


DETERMINATION  OF  LIMINAL  EXPOSURE. 

As  a  starting  point  in  our  experiments  it  was  necessary  to  determine, 
using  the  standard  source  just  described,  how  long  exposure  at  some 
known  distance  was  necessary  in  order  to  produce  clearly  marked 
symptoms  of  photophthalmia.  Our  experimentation  throughout  the 
work  has  been  chiefly  with  rabbits,  since  these  animals  have  been 
generally  used  by  other  experimenters  and  the  characteristics  of  their 
eyes  have  therefore  become  fairly  well  known. 


EFFECTS   OF   RADIANT   ENERGY   ON   THE   EYE.  639 

The  method  of  experimenting  was  as  follows:  The  animal  was 
enclosed  in  a  box  without  a  cover  through  one  end  of  which  the  head 
protruded,  being  held  in  place  by  a  sliding  end  piece.  The  eye  was 
held  open  by  a  Murdoch  speculum  made  of  proper  size  for  the  pur- 
pose, and  was  then  exposed  at  a  known  distance  from  the  quartz 
lamp  working  at  standard  intensity  for  a  given  period.  A  few  hours 
later,  usually  the  next  day, 'after  the  course  of  the  experiments  was 
settled,  careful  examination  was  made  of  the  external  eye  for  any 
signs  of  effect  from  the  radiation,  the  unexposed  eye  being  used  as  a 
check.  After  a  few  preliminary  trials  we  found  that  the  occurrence 
of  slight  conjunctivitis  was  less  readily  determinable  than  the  damage 
to  the  corneal  epithelium  showing  in  the  reflection  of  light  from  the 
cornea  by  a  slight  irregular  crackled  appearance  giving  way  after 
stronger  exposures  to  faint  stippling.  A  still  greater  severity  of 
exposure  produces  faint  haziness.  We  also  tried  staining  with  fluo- 
rescine  as  index  of  damage  to  the  epithelium,  but  found  in  the  first 
stages  disturbance  of  the  corneal  light  reflection  a  more  reliable  guide. 
This  indicates  a  somewhat  more  severe  exposure  than  produces  the 
first  trace  of  conjunctivitis,  but  its  presence  or  absence  is  quite  definite 
whereas  the  conjunctivitis  may  not  be  easy  to  determine  if  the  rabbit's 
eyes  are  naturally  somewhat  reddened. 

The  minimum  exposure  at  .5  meter  required  to  produce  the  first 
signs  of  pathological  change  on  the  surface  of  the  cornea  was  deter- 
mined to  be  six  minutes.  The  following  experiments  show  the  results 
leading  to  the  establishment  of  this  minimum,  and  it  will  be  seen  that 
the  liminal  period  was  sometimes  about  a  minute  shorter  or  longer, 
various  animals  differing  somewhat  in  sensitiveness.  It  will  be 
observed  that  to  produce  loss  of  corneal  epithelium  required  an  expo- 
sure about  2|  times  that  necessary  to  produce  slight  photophthalmia. 


EXPERIMENTS. 

Negative  results.     Exposures  in  minutes :  1;  1\\  3;  3;  3;  5;  5;  5;  1\. 

Slight  but  definite  conjunctivitis  with  impairment  of  corneal  light 
reflection.  Exposures  in  minutes :  7|;  5;  1\\  1\\  6;  6;  6;  1\\  6;  4 
(albinp). 

Marked  conjunctivitis  with  slight  haze  of  cornea  but  without  loss 
of  corneal  epithelium.  Exposures  in  minutes:  10;  10. 

Marked  conjunctivitis  with  haze  of  cornea  and  loss  of  corneal  epithe- 
lium. Exposure  in  minutes:  15. 


640  VERHOEFF  AND   BELL. 


VERIFICATION  OF  LAW  OF  INVERSE  SQUARES. 

The  outcome  of  this  series  of  experiments  was  that  radiation  from 
the  mercury  vapor  lamp  to  the  amount  of  4  X  10 6  erg-seconds  per 
square  cm.  is  required  to  set  up  the  first  definite  symptoms  of  photoph- 
thalmia.  This  assumes  that  the  effect  is  proportional  to  time,  in 
other  words,  that  the  pathological  results  are  determined  by  the  total 
amount  of  energy,  and  the  next  series  of  experiments  was  directed 
to  the  establishment  of  the  truth  or  falsity  of  this  assumption.  For 
this  purpose,  having  ascertained  the  liminal  exposure  for  a  single 
distance,  .5  meter,  exposures  were  made  at  various  distances  for  times 
computed  for  equal  total  radiation,  assuming  the  law  of  inverse 
squares  to  hold  for  the  relative  intensities.  For  example,  at  1  meter 
the  time  required  to  produce  the  determining  symptoms,  assuming 
the  law  of  inverse  squares,  should  be  four  times  that  required  for  .5 
meter,  which  was  found  to  be  closely  the  case.  By  repeated  experi- 
ments at  distances  varying  from  about  20  cm.  to  2.5  meters,  the  inverse 
square  law  was  verified  over  a  range  of  radiation  intensities  in  the 
ultra  violet  varying  from  72,000  ergs  per  square  cm.  per  second  down 
to  455  ergs  per  second  per  square  cm.,  at  a  range  in  other  words  of 
156  to  1.  For  any  source  yielding  rays  capable  of  producing  patho- 
logical effects  on  the  cornea  therefore,  the  exposure  time  required  to 
produce  symptoms  of  photophthalmia  is  inversely  proportional  to 
the  intensity  of  the  radiation  of  such  rays,  and  can  be  definitely  deter- 
mined when  the  intensity  of  the  damaging  radiation  is  known,  subject 
to  the  condition  that  if  the  computed  time  reaches  many  hours  it 
may  be  even  further  lengthened  by  the  intervention  of  physiological 
repair.  This  conclusion  is  of  fundamental  importance,  since  it  shows 
that  the  symptoms  are  due  to  or  are  proportional  to,  the  direct  and 
primary  effect  of  the  energy.  Since,  as  we  shall  show  later,  the  rays 
which  are  able  to  injure  cells  by  chemical  action  are  only  those  of 
wave  lengths  below  305  /z/z,  these  present  experiments  of  ours  show 
that  the  critical  amount  of  such  radiation  required  to  set  up  well 
marked  photophthalmia  is  approximately  2  X  10 6  erg-seconds  per 
square  cm.  In  other  words  only  half  of  the  total  ultra  violet  already 
specified  is  effective  in  producing  such  symptoms. 

A  close  general  relation  between  the  amount  of  incident  energy  and 
its  effects  on  the  cornea  was  beautifully  shown  by  the  results  obtained 
after  relatively  severe  exposures.  In  such  cases  after  the  symptoms 
had  developed  there  was  a  distinct  haziness  confined  chiefly  to  the 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          641 

central  portion  of  the  cornea  and  rapidly  shading  off  toward  the 
periphery,  where,  as  is  shown  in  Figure  2,  the  energy  received  per  unit 
area  is  greatly  decreased.  Thus  the  mere  appearance  of  the  affected 
area  shows  in  a  qualitative  way  proportionality  between  the  exposure 
and  the  following  lesion,  a  proportionality  shown  to  be  definite  in  the 
experiments  we  have  described. 


THE  EFFECTS  OF  REPEATED  EXPOSURES  TO  ABIOTIC  RADIATIONS. 

A  natural  corollary  of  the  proposition  that  the  pathological  effects 
of  abiotic  rays  on  the  cornea  are  proportional  to  the  energy  is  that  at 
least  for  brief  intermissions  the  effects  of  repeated  short  exposures 
are  equivalent  to  their  sum  in  a  single  long  exposure.  This  is,  of 
course,  subject  to  the  general  qualification  that  reparative  processes 
are  steadily  going  on,  tending  rather  gradually  to  the  healing  of 
injured  tissue.  An  ordinary  case  of  photophthalmia  completely 
disappears  in  less  than  a  week  and  repair  is  going  on  all  through  this 
period.  It  is  obviously  possible  also  that  apparent  complete  recovery 
may  still  leave  the  tissues  slightly  hypersensitive  to  further  injury. 
We  therefore  set  about  investigating  the  effects  of  repeated  exposures, 
both  liminal  and  subliminal,  to  ascertain  the  additive  effect  of  short 
exposures,  the  rate  at  which  the  reparative  processes  proceeded,  the 
completeness  of  their  work,  and  the  possible  effects  of  secondary 
reactions  incidental  to  the  main  pathological  effects.  There  was  a 
bare  possibility  that  something  akin  to  anaphylaxis  might  occur 
owing  to  the  development  of  toxins,  and  this  phase  of  the  matter  had 
also  to  be  investigated. 

In  the  case  of  abiotic  radiation  affecting  a  large  portion  of  the  body 
i  t  seems  possible  that  a  general  constitutional  effect  might  occur  owing 
to  the  absorption  of  the  toxic  substances  produced.  Such  an  effect 
is  known  to  occur  after  severe  burns  from  heat.  In  the  case  of  the 
eye,  however,  the  amount  of  tissue  affected  is  of  course  too  slight 
for  any  such  effect  to  be  expected. 

The  experiments  on  subliminal  exposures  repeated  at  intervals  of  a 
few  minutes  to  an  hour  or  more,  here  summarized,  show  clearly  that 
within  24  hours  the  energy  effects  are  simply  additive,  intermissions 
within  this  time  evidently  being  too  short  for  reparative  action  to 
take  place.  The  discovery  of  this  fact  is  important  since  it  shows  that 
with  any  source  of  abiotic  rays  it  is  the  total  exposure  that  counts, 
and  that  the  effect  of  this  total  exposure,  if  within  24  hours,  can  be 
calculated  from  the  data  already  given. 


642  VERHOEFF   AND    BELL. 


EXPERIMENTS. 

EFFECT  OF  REPEATED  EXPOSURES.     QUARTZ  MERCURY  VAPOR  LAMP 
DISTANCE  .5  METER. 

Subliminal  Exposures  Repeated  within  24  Hours. 

Experiment  23.  Right  eye.  Exposure  3f  minutes.  Interval 
10  minutes.  Exposure  3f  minutes.  Left  eye.  Exposed  7|  min- 
utes continuously.  Result:  Reaction  in  both  eyes,  more  marked 
in  right. 

Experiment  24.  Right  eye.  Exposed  five  minutes  with  four 
intervals  of  one  minute  each.  Left  eye.  Exposed  5  minutes  continu- 
ously. Result:  Very  slight  reaction  in  each  eye. 

Experiment  25.  Right  eye.  Exposed  3  minutes.  One  hour  inter- 
val. Exposed  3  minutes.  Result:  Marked  reaction. 

Experiment  26.  Right  eye  exposed  3  minutes.  Four  hours  inter- 
val. Exposed  3  minutes.  Result:  Marked  reaction. 

The  next  phase  of  the  investigation  dealt  with  subliminal  exposures 
at  intervals  of  one  or  more  days,  such  as  might  occur  in  actual  use  of 
sources  rich  in  abiotic  radiation.  The  results  show  that  an  exposure 
of  one-sixth  the  liminal  repeated  every  24  hours  for  52  days  has  no 
visible  effect  on  the  cornea  or  conjunctiva.  An  exposure  of  one-third 
the  liminal  repeated  every  48  hours  has  a  slight  effect  on  the  cornea 
after  seven  to  nine  exposures,  which  however  gradually  disappears 
in  spite  of  the  exposures  being  continued.  A  daily  exposure  of  one- 
third  the  liminal  begins  to  produce  a  reaction  after  six  exposures. 
The  conjunctivitis  disappears,  but  the  corneal  effect  gradually  in- 
creases until  after  thirty -four  exposures  there  is  a  marked  central  haze. 
This  leaves  a  slight  corneal  scar  which  is  barely  visible  forty  days  after 
the  last  exposure.  An  exposure  one-half  the  liminal  repeated  at  the 
end  of  24  hours  produces  the  effect  of  a  single  liminal  exposure.  A 
single  exposure  just  subliminal,  increases  the  sensitiveness  of  the  eye 
to  abiotic  radiation  for  over  two  weeks.  On  the  other  hand  an 
exposure  one-sixth  the  liminal  every  24  hours,  or  one-third  the  liminal 
every  48  hours  repeated  for  a  long  period  of  time,  has  the  effect  of 
rendering  the  eye  somewhat  less  sensitive  to  abiotic  action. 


EFFECTS   OF   RADIANT   ENERGY   ON  THE   EYE.  643 


EXPERIMENTS. 

Subliminal   Exposures    Repeated   after   24   Hours.     Quartz    Mercury 
Vapor  Lamp.     Distance  .5  Meter. 

Experiment  27.  Right  eye.  Exposed  1  minute  every  day  except 
Sunday  for  52  days.  (44  exposures.)  Result:  No  reaction  through- 
out the  experiment.  Three  days  after  last  exposure;  each  eye 
exposed  six  minutes.  Result:  Moderate  reaction  in  each  eye,  but 
greater  in  the  left  eye. 

Experiment  28.  Left  eye.  Exposed  2  minutes  every  other  day, 
except  when  Sunday  intervened.  Results:  After  7  exposures,  slight 
stippling  of  corneal  surface.  After  9  exposures,  slight  haze  of 
cornea.  After  11  exposures,  haze  of  cornea  gone.  After  28  expos- 
ures, cornea  clear,  no  stippling.  After  33  exposures  cornea  clear, 
exposures  discontinued.  Nine  days  later,  each  eye  exposed  six  min- 
utes. Results:  Right  eye,  marked  reaction.  Left  eye,  much  less 
reaction. 

Experiment  29.  Left  eye.  Exposed  2  minutes  every  day  except 
Sunday.  A  speculum  was  used  at  first  but  caused  ectropion  of  the 
lid  and  was  soon  dispensed  with.  Results:  No  reaction  until  sixth 
exposure  when  there  was  slight  conjunctivitis  and  stippling  of  the  cor- 
nea. After  14  exposures  the  conjunctival  reaction  had  disappeared 
but  the  cornea  was  distinctly  hazy  in  the  centre.  After  34  exposures 
the  central  haze  of  the  cornea  was  marked  and  the  epithelial  surface 
showed  a  number  of  fine  irregular  ridges.  Exposures  discontinued. 
Forty  days  later  only  a  barely  visible  opacity  of  the  cornea  remained. 
Enucleation.  Microscopic  examination  shows  Bowman's  membrane 
absent  in  places,  and  proliferation  and  irregular  arrangement  of  the 
superficial  corneal  corpuscles. 

Experiment  30.  Left  eye  exposed  3  minutes.  After  24  hours,  no 
reaction.  Left  eye  exposed  3  minutes.  Right  eye  exposed  6  minutes. 
Results :  Reactions  equal  in  two  eyes. 

Experiment  31.  Right  eye  exposed  5  minutes.  Result:  No  re- 
action. Two  weeks  later.  Right  eye  exposed  4  minutes.  Result: 
Slight  reaction. 

The  next  series  of  experiments  had  to  do  with  the  effect  of  previous 
reactions  upon  the  sensitiveness  of  the  eye  to  subsequent  exposures. 
It  was  found  that  previous  reactions  rendered  the  eye  more  sensitive 
for  at  least  one  month,  thus  reducing  the  time  of  exposure  necessary 


644  VERHOEFF  AND   BELL. 

for  a  liminal  reaction.  It  was  found  also  that  if  an  exposure  sufficient 
to  produce  a  slight  reaction,  was  followed  within  24  hours  by  a  sub- 
liminal exposure,  the  total  effect  was  considerably  greater  than  that 
produced  in  the  control  eye  by  a  continuous  exposure  of  the  same 
total  length. 

EXPERIMENTS. 

EFFECT  OF  PREVIOUS  REACTIONS  UPON  SENSITIVENESS  OF  EYE  TO 
SUBSEQUENT  EXPOSURES.     QUARTZ  MERCURY  VAPOR  LAMP. 

Experiment  32.  Distance  .5  meter.  Albino  rabbit.  Right  eye 
exposed  4  minutes.  After  24  hours,  slight  reaction  (animal  unusually 
sensitive).  Right  eye  exposed  2  minutes.  Left  eye  exposed  6  min- 
utes. Results:  Right  eye,  increased  reaction  with  loss  of  corneal 
epithelium.  Left  eye,  moderate  reaction  without  loss  of  corneal 
epithelium. 

Experiment  33.  Distance  .5  meter.  Right  eye  exposed  5  minutes. 
Result:  Very  slight  reaction.  One  month  later.  Right  eye  exposed 
3^  minutes.  Result:  Moderate  conjunctivitis,  marked  stippling  of 
cornea. 

Experiment  34.  Right  eye  exposed  5  minutes  at  .5  meter.  Left 
eye  exposed  1\  minutes  at  .5  meter.  Results:  No  reaction  in  either 
eye.  14  days  later.  Right  eye  exposed  forty  minutes  at  35  cm. 
through  crown  screen.  Left  eye  exposed  4  minutes  at  35  crn.  with- 
out screen.  Results:  Slight  reactions,  more  marked  in  left  eye.  8 
days  later.  Right  eye  exposed  3  minutes  at  .5  meter.  Left  eye 
exposed  4  minutes  at  .5  meter.  Results:  Slight  reaction  in  each  eye. 
More  marked  in  right. 

Experiment  35.  Distance  .5  meter.  Left  eye  exposed  1\  minutes. 
Result:  Reaction.  26  days  later.  Left  eye  exposed  4  minutes. 
Result:  Slight  reaction. 

Experiment  36.  Right  eye  exposed  1^  hours  at  20  cm.  through 
crown  screen.  Result:  Marked  reaction  with  keratitis,  lasting  over 
2  weeks.  5  weeks  later.  Left  eye  exposed  2  minutes  at  .5  meter. 
Result:  No  reaction. 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE. 


645 


DETERMINATION  OF  THE  LIMIT  OF  ABIOTIC  ACTION  WITH  RESPECT 
TO  WAVE  LENGTH. 

The  critical  wave  length  at  which  abiotic  action  on  tissue  cells 
ceases  has  not  hitherto  been  accurately  determined.  For  bacteria 
it  has  been  found  to  be  about  wave  length  295  MM-  In  this  connection 
the  observations  of  Henri 163  and  his  wife  are  important.  These 
observers  determined  the  coefficient  of  absorption  of  egg  albumin  for 
various  wave  lengths  and  found  that  the  results  corresponded  closely 


250 

Wave  length 

FIGURE  3.     Variation  of  abiotic  power  with  wave  length. 
Henri's  results). 


(Plotted  from 


with  the  time  value  of  bactericidal  action  for  the  wave  lengths  tested. 
The  curve  of  absorption  plotted  from  their  results  (Fig.  3)  shows 
that  the  abiotic  action  of  light  with  reference  to  wave  length  may  be 
expected  to  diminish  rapidly  and  terminate  at  about  310  MM-  The 
experiments  of  Widmark,  Hess,  and  Martin,  in  which  the  lens  epi- 


646  VERHOEFF  AND   BELL. 

thelium  was  injured  by  exposures  through  the  cornea,  prove  con- 
clusively that  295  MM  is  not  the  limit  for  human  cells,  since  the  cornea 
obstructs  all  waves  less  than  295  MM  in  length.  It  has  frequently 
been  assumed  that  there  is  no  actual  limit  of  abiotic  action  but  that 
the  latter  exists  in  a  diminishing  degree  through  the  entire  spectrum. 
Theoretically  this  may  be  true,  but  practically  it  is  not,  as  our  experi- 
ments show,  and  for  the  following  two  reasons,  namely,  first,  that  in 
the  case  of  the  longer  waves  and  moderate  light  intensities  the  abiotic 
action  is  so  slight  as  to  be  readily  overcome  by  the  physiological  activi- 
ties of  the  cells,  and  second, 'that  in  the  case  of  the  longer  waves  and 
intensities  theoretically  sufficient  to  produce  abiotic  effects  the  cells 
are  destroyed  by  heat  action,  so  that  there  is  no  opportunity  for 
abiotic  effects  to  become  manifest.  The  real  problem  may  therefore 
be  stated  to  be  the  determination  of  the  critical  wave  length  for 
abiotic  action  with  light  intensities  just  below  those  sufficient  to  pro- 
duce  injurious  heat  effects. 

For  the  experimental  investigation  of  this  problem  the  cornea  and 
lens  are  of  all  the  tissues  of  the  body  the  most  suitable.  This  is  so 
because,  owing  to  their  great  transparency,  extreme  light  intensities 
are  required  to  produce  heat  effects  in  them  sufficient  to  mask  abiotic 
effects.  The  conjunctiva  and  skin  are  far  less  suitable  for  this  purpose 
because  when  the  limit  of  abiotic  action  with  respect  to  wave  length 
is  approached  the  hyperemia  due  to  heat  action  overshadows  that 
due  to  abiotic  action. 

In  this  investigation  it  was  necessary  to  abandon  the  use  of  the 
quartz  mercury  lamp  employed  in  the  earlier  experiments.  As 
already  noted  the  spectrum  of  this  source  has  conspicuous  gaps  in  the 
very  region  to  be  examined  for  the  purpose  in  hand.  It  has  no  lines 
of  perceptible  intensity  between  334  MM  and  the  strong  double  line  at 
313  MM-  Then  there  is  a  further  gap  extending  down  to  the  group 
having  its  center  about  302.5  MM  and  another  between  this  group  and 
297  MM-  In  fact  there  are  only  three  rather  widely  separated  lines 
in  this  entire  debatable  region  within  which  the  limit  sought  was 
known  to  lie.  We  therefore  turned  to  the  commercial  magnetite 
arc  as  the  most  convenient  available  source  since  this  had  already 
been  found  by  one  of  us  to  be  particularly  rich  in  the  extreme  ultra 
violet.  This  lamp  uses  as  active  electrode  an  iron  tube  carrying  a 
compressed  mixture  of  magnetite  and  of  titanium  oxide,  in  a  pro- 
portion of  about  3  of  the  former  to  1  of  the  latter,  opposed  to  a  copper 
positive  electrode.  The  light  is  practically  all  derived  from  the  arc 
stream  produced  by  the  magnetite  electrode.  The  spectrum  of  this 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          647 

source  is  enormously  rich  in  lines  due  to  a  complex  mixture  of  those 
belonging  to  iron  and  titanium,  reaching  down  to  waves  below  230  MM- 
Moreover,  the  spectrum  is  particularly  rich  in  lines  between  330  MM 
and  290  MM-  Beyond  this  the  intensity  falls  off  noticeably.  The 
source  is  thus  particularly  well  adapted  for  work  in  the  region  here 
investigated.  The  lamp  used  took  approximately  9  amperes  at  the 
arc  which  consumed  approximately  750  watts.  The  energy  in  the 
ultra  violet  from  wave  length  390  MM>  was  about  15,000  ergs  per 
second  per  square  cm.  at  .5  meter  standard  distance,  of  which  approxi- 
mately 3500  ergs  was  below  300  MM>  as  against  very  nearly  5700  ergs 
per  second  per  square  cm.  for  the  quartz  lamp  in  the  same  region. 
The  latter  source,  however,  as  just  pointed  out  has  relatively  more 
energy  in  the  shorter  wave  lengths.  Plate  5  shows  side  by  side  the 
spectra  of  the  two  sources  in  the  ultra  violet. 

For  determining  the  wave  length  at  which  abiotic  effects  on  the 
cornea  and  lens  cease,  the  use  of  suitable  screens  is  very  much  prefer- 
able to  attempts  at  using  the  spectrum  formed  by  a  quartz  prism  as  the 
source  of  energy.  This  is  for  the  reason  that  with  screens  one  can 
obtain  an  enormously  greater  amount  of  energy  than  it  is  practicable 
to  get  by  passing  the  radiation  through  a  slit,  collimating  lens  and 
prism,  especially  in  cases  where  a  considerable  area  like  that  of  the 
cornea  must  be  covered.  In  our  experiments  seven  screens  were 
employed  of  which  the  absorption  was  definitely  ascertained  by  the 
spectrograph.  These  screens  were  of  various  sorts  of  optical  glass 
and  mostly  in  the  form  of  discs  43  mm.  in  diameter  and  2  mm.  thick. 
They  were  as  follows: — 

Limits  of  absorption 

1.  Extra  dense  flint  ND     1.69  335  MM 

2.  Medium  flint  ND     1.62  315  MM 

3.  Medium  flint  ND     1.616,  1  mm.  thick.  310  MM 

4.  Light  flint  ND     1.57  305  MM 

5.  Medium  crown  ND  approximately  1.52  300  MM 

6.  Extra  light  flint  ND     1.54  298  MM 

7.  Light  crown  ND     1.51  295  MM 

The  absorption  of  these  seven  glasses  for  the  magnetite  spectrum 
is  shown  in  Plate  6  with  the  scale  of  wave  lengths  subjoined.  These 
limits  are  taken  at  the  point  where  the  transmission  somewhat  ab- 
ruptly ceases.  They  do  not  run  to  the  last  lines  of  which  traces  are 
visible,  since  these  are  so  immensely  reduced  by  the  absorption  as  to 
have  little  if  any  effect  bearing  on  the  experiments.  In  any  case  the 


<B48  VERHOEFF  AND   BELL. 

error  would  be  in  the  direction  of  safety,  that  is,  it  would  tend  to 
set  the  limit  of  abiotic  action  at  too  long  a  wave  length.  It  will  be 
noted  that  in  this  series  of  screens  the  transmission  grades  off  with 
considerable  regularity. 

In  addition  to  these  screens  the  following  absorbing  media  were 
used  in  some  of  the  experiments.  These  did  not  prove  of  value  in 
determining  the  limits  of  abiotic  action,  but  are  described  here  because 
the  experiments  in  which  they  were  used  are  important  in  reference 
to  possible  retinal  effects,  owing  to  the  long  exposures  given.  (Plate  5.) 

Material  Limit  of  Absorption 

8.  CuCU  1.5%  solution  in  5  cm.  quartz 

cell  320  MM,  beyond  700  MM 

9.  Blue  Uviol  glass  2  mm.  285  MM  and  beyond  470  MM 

10.  Auramine  O  .001%  solution  in  5  cm. 

quartz  cell  250  MM>  400  MM  to  450  MM 

11.  (9+10) 

Auramine  O,  which  we  tried  in  several  concentrations,  is  remarkable 
for  the  freedom  with  which  it  transmits  the  extreme  ultra  violet  while 
absorbing  the  violet  end  of  the  visible  spectrum  rather  strongly. 

For  producing  intensive  exposures,  and  particularly  for  work  on 
the  retina  the  magnetite  arc  here  described  was  reenforced  by  the 
use  of  a  quartz  lens  system.  For  one  set  of  experiments  we  employed 
two  piano  convex  quartz  lenses  each  of  42  mm.  diameter  and  18  cm. 
focal  length.  These  two  were  generally  employed  placed  with  the 
plane  faces  in  contact  either  with  each  other  or  with  one  of  our  screens, 
making  in  fact  a  single  lens  of  9  cm.  focal  length  for  parallel  rays. 
This  lens  was  placed  20  cm.  from  the  arc,  an  image  of  which  was  formed 
14  cm.  beyond  it,  at  which  point  the  eye  was  placed.  In  this  set  of 
experiments  in  addition  to  abiotic  effects  in  the  cornea  and  lens, 
small  circumscribed  heat  effects  were  obtained  in  the  retina  analogous 
to  those  of  eclipse  blindness.  These  will  be  discussed  later  (page  697). 
In  another  set  of  experiments  the  apparatus  was  assembled  as  shown 
in  Figure  4.  The  lenses  referred  to,  B,  were  placed  at  12  cm.  from  the 
arc  flame  A.  In  the  converging  cone  of  rays  produced  by  B,  was 
placed  at  a  distance  of  12  cm.  therefrom  a  double  convex  lens  C  of 
quartz  cut  across  the  axis,  23  mm.  in  diameter  and  of  14  mm.  focal 
length  for  parallel  rays.  In  the  combination  used,  C  brought  the 
rays  to  a  focus  at  about  12  mm.  from  its  outer  apex  at  or  near  which 
point  the  cornea  of  the  eye  D  was  located  in  the  experiments.  The 


EFFECTS    OF   RADIANT   ENERGY   ON   THE    EYE. 


G49 


path  of  the  rays  is  shown  by  the  dotted  lines  in  the  figure.  The  effect 
of  the  arrangement  was  to  pass  through  the  cornea  a  strongly  diverg- 
ing pencil  producing  a  circle  of  intense  light  on  the  retina.  The  axial 
length  of  the  ordinary  rabbit's  eye  is  about  16.5  mm.  and  the  ordinary 
diameter  of  the  area  of  intense  illumination  produced  by  our  appara- 
tus was  about  11  mm.  at  the  retina  as  was  determined  by  actual 
experiment  upon  a  freshly  removed  eye.  With  this  apparatus  a  large 
amount  of  energy  could  be  concentrated  on  any  required  area  at  or 
within  the  surface  of  the  cornea  or  lens,  and  by  aid  of  these  lens  sys- 
tems we  were  able  to  obtain  exposures  enormously  more  severe  than 
could  possibly  be  obtained  from  artificial  light  sources  in  ordinary  use 
or  than  have  ever  been  obtained  by  previous  experimenters  in  this 
field.  The  image  was  kept  fixed  during  the  exposure  by  slight 
shifting  of  the  source  or  lens,  since  the  arc  itself  tends  to  wander. 

By  the  use  of  photo  paper  the  following  data  were  obtained  con- 
cerning the  relative  intensities  of  radiation  at  the  focus  and  on  the 
retina  with  the  double  lens  system.  The  size  of  the  area  of  most 


— T\ — 

\  — — ————__ 


FIGURE  4.     Quartz  condensing  system.     Screens  omitted  for  simplicity. 


intense  illumination  at  the  focus  was  2  X  4j  mm.  The  diameter 
of  effective  illumination  at  a  distance  of  16  mm.  from  the  focus, 
corresponding  to  the  position  of  the  retina,  was  11  mm.  Through 
a  euphos  glass  screen  an  exposure  of  5  seconds  at  the  focus  closely 
corresponded  in  intensity  to  an  exposure  of  75  seconds  at  the  position 
of  the  retina,  so  that  neglecting  absorption  by  the  media  of  the  eye  the 
intensity  of  the  illumination  of  the  retina  with  this  lens  system  was 
about  fifteen  times  less  than  that  of  the  cornea.  This  ratio  was  con- 
firmed by  photographs  taken  with  a  model  schematic  eye  without 
screen  and  with  a  picric  acid  screen,  so  that  it  may  be  assumed  to  hold 
over  a  very  wide  range  of  wave  lengths. 

The  results  of  these  experiments  are  given  below.  For  purposes  of 
comparison  other  experiments  with  the  magnetite  are  also  given  here, 
although  they  have  no  direct  bearing  on  the  determination  of  the 
critical  wave  length  of  abiotic  action.  For  the  same  reason  experi- 
ments are  given  showing  the  length  of  exposure  to  the  quartz  mercury 


650  VERHOEFF  AND   BELL. 

vapor  lamp  through  a  crown  screen  (295  MM)  necessary  to  produce 
photophthalmia.  The  thermic  effects  produced  in  these  experiments 
as  well  as  the  character  of  the  abiotic  effects  are  discussed  elsewhere 
(pages  662  and  692). 

For  determining  the  critical  wave  length  of  abiotic  action  it  will  be 
seen  that  the  crucial  experiments  were  Experiments  81  to  85.  These 
showed  that  for  light  of  extreme  intensity  no  effects  either  abiotic 
or  thermic,  were  produced  on  the  cornea  or  lens  epithelium  by  an 
exposure  of  1|  hours  to  waves  over  315  MM  m  length,  and  that  no 
abiotic  effects  but  slight  thermic  effects  were  produced  by  light  con- 
taining wave  lengths  of  310  MM  and  longer.  Light  containing  wave 
lengths  of  305  MM  and  longer,  produced  marked  thermic  effects  but 
no  abiotic  effects  after  one  hour  exposure,  but  after  1^  hours  exposure 
produce  marked  thermic  effects  and  the  slightest  possible  trace  of 
abiotic  effects.  That  is  to  say,  the  limit  of  abiotic  action  with  refer- 
ence to  wave  length  for  corneal  cells  is  almost  exactly  305  MM-  In 
Experiment  82,  in  which  the  light  was  focussed  on  the  cornea,  the  only 
evidence  of  abiotic  action  was  the  loss  of  corneal  epithelium,  while 
in  the  Experiment  83,  in  which  the  light  was  focussed  on  the  anterior 
surface  of  the  lens,  the  only  evidences  of  such  action  were  the  slight 
but  characteristic  changes  in  the  lens  epithelium.  In  any  other 
available  tissues  than  the  cornea  and  lens  such  slight  abiotic  effects 
would  undoubtedly  have  been  completely  masked  by  extreme  heat 
effects,  but  in  none  of  these  experiments  did  the  lens  show  the  slight- 
est thermic  effects. 

The  insignificance  of  the  abiotic  action  at  wave  length  305  MM 
becomes  more  apparent  when  the  equivalent  critical  time  is  computed 
for  exposure  to  the  direct  radiations  from  the  magnetite  arc.  Our 
experiments  show  that  the  intensity  of  light  at  the  focus  of  the  double 
lens  system  is  at  least  eighteen  times  the  intensity  of  the  bare  arc  at  a 
distance  of  20  cm.  This  means  that  to  obtain  slight  loss  of  corneal 
epithelium  with  direct  waves  of  305  MM  m  length  from  the  magnetite 
arc,  an  exposure  of  27  hours  at  a  distance  of  20  cm.  or  an  exposure 
of  28  days  at  a  distance  of  1  meter  would  be  required.  To  produce 
mild  photophthalmia  the  time  required  would  be  about  one-third 
these  figures.  As  a  matter  of  fact  however,  our  experiments  on 
frequently  repeated  subliminal  exposures,  already  given,  prove  that 
at  1  meter  no  effects  whatever  would  be  produced  by  such  slight 
abiotic  action  per  unit  of  time  owing  to  the  vital  activities  of  the  cells. 

Similar  calculations  for  the  portion  of  the  spectrum  including 
only  waves  longer  than  295  MM>  as  well  as  direct  experiments,  show  that 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          651 

an  exposure  of  20  minutes  at  20  cm.,  in  case  of  the  magnetite  arc, 
is  required  to  produce  photophthalmia,  or  an  exposure  of  85  hours 
at  1  meter.  The  ratio  of  the  abiotic  activity  of  the  whole  spectrum 
to  that  of  the  portion  exceeding  295  wu  is  ^p .  This  holds  approxi- 
mately true  also  for  the  quartz  mercury  vapor  lamp. 

In  regard  to  the  lens  epithelium,  it  should  be  noted  that  only 
abiotic  changes  were  obtained,  and  these  with  wave  lengths  as  long 
as  305  up  as  already  stated.  With  light  of  this  wave  length,  however, 
as  shown  by  the  above  computation  it  is  evident  that  they  could  not 
be  obtained  by  means  of  the  direct  light  from  any  artificial  light 
sources  at  any  distance  at  which  the  eye  could  bear  the  heat.  With 
wave  lengths  of  295  fj-n  and  over,  the  lens  epithelium  was  affected  by 
an  exposure  of  5  minutes  to  the  double  lens  system,  the  liminal  expo- 
sure probably  being  about  3  minutes.  Since  the  cornea  itself  cuts  off 
the  waves  at  this  point,  it  follows  that  an  exposure  to  the  bare  mag- 
netite arc  of  54  minutes  at  20  cm.  or  of  22  hours  at  1  meter  would  be 
required  to  affect  the  lens  epithelium.  Hess,  strangely  enough,  was 
unable  to  obtain  lens  changes  through  a  screen  transparent  to  waves 
of  280  H/JL,  and  drew  the  inconsistent  conclusion,  in  view  of  the  fact 
that  the  cornea  was  known  by  him  to  obstruct  still  longer  waves, 
that  lens  changes  are  produced  only  by  the  very  short  waves  of  the 
spectrum.  The  character  of  the  lens  changes  produced  in  our  experi- 
ments is  described  on  page  671. 

Judging  by  the  effects  on  the  cornea,  the  abiotic  intensity  at  the 
focus  for  the  single  lens  system  was  about  ^  that  for  the  double  lens 
system. 

Comparing  the  results  obtained  with  the  quartz  mercury  vapor 
lamp  and  those  with  the  magnetite  arc  it  is  found  that  the  abiotic 
activity  of  the  entire  spectrum  of  each  is  in  about  the  ratio  of  6  for 
the  mercury  lamp  to  5  for  the  magnetite  arc.  This  ratio  holds  with 
and  without  the  crown  screen  (295juju). 

These  ratios  obtained  from  the  pathological  effects  are  in  fairly 
close  accord  with  those  derived  from  the  experiments  of  one  of  us  by 
purely  radiometric  methods.  Taking  average  conditions  of  the  two 
sources  here  referred  to,  the  abiotic  radiations  from  the  quartz  lamp 
should  aggregate  about  4200  ergs  per  second  per  square  cm.  at  the 
standard  distance  of  .5  meter.  The  magnetite  arc  as  used  gave  abio- 
tic radiations  aggregating  about  3300  ergs  per  second  per  square  cm. 
at  the  same  distance.  The  ratio  between  these  two  quantities  is 
5  to  6.35  as  compared  with  the  5  to  6  of  the  pathological  results,  an 
agreement  quite  as  close  as  could  reasonably  be  expected  considering 
the  nature  of  the  case. 


652  VERHOEFF  AND   BELL. 

Full  grown  rabbits  were  used  in  all  the  experiments  and  the  light 
was  focussed  upon  the  cornea  unless  otherwise  stated.  In  all  experi- 
ments relating  to  the  retina  the  pupil  was  previously  dilated  by  a 
mydriatic.  In  the  experiments  with  the  double  lens  system  the  con- 
junctiva was  not  directly  exposed  to  the  light  so  that  the  conjuncti- 
vitis noted  was  largely  secondary.  The  iris  however  was  sometimes 
more  or  less  exposed. 

EXPERIMENTS. 

QUARTZ   MERCURY   VAPOR   LAMP.      CROWN   GLASS   SCREEN    (295  MJL). 

Distance  35  cm. 

Experiment  37.     Exposed  20  minutes.     No  reaction. 

Experiment  38.     Exposed  40  minutes.     Little  if  any  reaction. 

Experiment  39.     Exposed  40  minutes.     Little  if  any  reaction. 

Experiment  40.  Exposed  60  minutes.  Moderate  conjunctivitis. 
Cornea  clear.  Iris  congested. 

Distance  20  cm. 

Experiment  41.  Exposed  1|  hours.  Marked  purulent  conjuncti- 
vitis. Cornea  very  hazy  in  central  area.  Iris  congested  and  hem- 
orrhagic.  The  conjunctivitis  persisted  about  10  days.  The  corneal 
haze  and  a  few  minute  iris  hemorrhages  were  visible  over  4  weeks. 


MAGNETITE   ARC.       NO    LENSES   OR   SCREENS. 

Experiment  42.  Distance  50  cm.  Exposed  6  minutes.  Slight 
conjunctivitis.  Stippling  of  corneal  surface  without  loss  of  epi- 
thelium. (Liminal  reaction.) 

Experiment  43.  Distance  20  cm.  Exposed  1  minute.  Slight 
conjunctivitis.  Corneal  epithelium  intact. 

Experiment  44.  Exposed  2|  minutes.  Moderate  purulent  con- 
junctivitis. Cornea  stippled  but  epithelium  intact. 

Experiment  45.  Exposed  4  minutes.  Marked  conjunctivitis  with 
edema  and  punctate  hemorrhages.  Cornea  hazy  and  epithelium  lost 
from  f  of  its  surface.  Microscopic  examination  (48  hrs.)  shows 
leucocytic  infiltration  of  cornea,  but  corpuscles  and  endothelium 
normal.  Lens  epithelium  normal. 

Experiment  46.  Exposed  15  minutes.  Marked  conjunctivitis. 
Haze  of  cornea  with  loss  of  epithelium.  Microscopic  examination 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          653 

(48  hrs.) ;  shows  leucocytic  infiltration  of  cornea.  Corpuscles  slightly 
affected  in  outermost  layers.  Endothelium  normal.  Lens  epithe- 
lium normal.  Iris  normal.  Serum  in  anterior  chamber. 

Experiment  47.  Exposed  16  minutes.  Result  same  as  in  previous 
experiment. 

MAGNETITE   ARC.      CROWN    GLASS   SCREEN    (295 /i/z). 

Experiment  48.  Distance  20  cm.  Exposed  20  minutes.  Slight 
conjunctivitis.  Cornea  clear,  not  stippled,  epithelium  intact. 

Experiment  49.  Distance  20  cm.  Exposed  40  minutes.  Well 
marked  conjunctivitis  with  edema  and  slight  purulent  discharge. 
Cornea  clear.  Reflex  impaired,  but  epithelium  intact  —  does  not 
stain. 

Experiment  50.  Water  cell.  Distance  14  cm.  Exposed  22  min- 
utes. Moderate  conjunctivitis.  Corneal  epithelium  intact.  Micro- 
scopic examination  (48  hrs.).  Cornea,  iris,  and  lens  epithelium 
normal.  No  serum  in  anterior  chamber. 


MAGNETITE   AEC.       QUARTZ    SINGLE    LENS   SYSTEM.      WATER    CELL. 

Experiment  51.  Albino.  Crown  glass  screen  (295  /JL/JL).  Exposed 
20  minutes.  Immediate  enucleation.  Microscopic  examination  shows 
cornea,  iris,  and  lens  epithelium  normal. 

Experiment  52.  Pigmented  eye.  Crown  glass  screen  (295  nn). 
Exposed  6  minutes.  Moderate  conjunctivitis.  Slight  haze  of  cornea 
without  loss  of  epithelium.  Microscopic  examination  (4  days): 
Corneal  stroma  shows  slight  leucocytic  infiltration.  Corpuscles  and 
endothelium  normal.  Lens  epithelium  normal. 

Experiment  53.  (PI.  4,  Fig.  12).  Albino.  Crown  glass  screen 
(295  ju/z).  Exposed  12  minutes.  Purulent  conjunctivitis.  Cornea 
hazy,  shows  loss  of  epithelium.  Iris  congested  and  hemorrhagic. 
Microscopic  examination  (48  hrs.):  Corneal  corpuscles  show  marked 
abiotic  changes.  Endothelium  absent.  Iris  shows  interstitial  hem- 
orrhages. Lens  epithelium  shows  moderate  abiotic  changes.  Retina 
shows  burned  spot. 

Experiment  54.  (PI.  3,  Fig.  9).  Albino.  Crown  glass  screen 
(295juju).  Exposed  20  minutes.  Marked  reaction  with  loss  of  corneal 
epithelium.  Microscopic  examination  (2  days) :  Most  of  the  corneal 
corpuscles  destroyed  in  central  area,  endothelium  absent.  Marked 
abiotic  changes  in  lens  epithelium.  Iris  shows  interstitial  hemorrhages. 


654  VERHOEFF  AND   BELL. 

Experiment  55.  (PI.  2,  Fig.  5).  Albino.  Crown  glass  screen 
(295  ju/z).  Exposed  1'hour.  Marked  reaction  with  loss  of  epithelium. 
Microscopic  examination  (24  hrs.) :  Corneal  corpuscles  destroyed  in 
central  area,  endothelium  absent,  marked  abiotic  changes  in  lens 
epithelium.  Iris  shows  interstitial  hemorrhages  and  slight  purulent 
exudation  from  vessels.  Retina  shows  burned  area. 

Experiment  56.  Pigmented  eye.  No  screen.  Exposed  20  minutes. 
Marked  reaction  with  loss  (f)  of  corneal  epithelium.  Beginning 
vascularization  of  cornea  on  6th  day.  Microscopic  examination  (6 
days):  Corneal  epithelium  reformed,  corpuscles  largely  destroyed, 
endothelium  absent.  Lens  epithelium  shows  marked  changes. 
Iris:  Most  of  the  stroma  cells  destroyed  in  anterior  half  of  iris  for  a 
distance  of  1.5  mm.  from  the  pupillary  margin.  Some  of  the  stroma 
cells  show  characteristic  granules.  A  few  mitotic  figures  seen.  Endo- 
thelium entirely  absent  from  some  of  the  blood  vessels.  Interstitial 
hemorrhages. 

Experiment  57.  Albino.  Crown  glass  screen  (300  MM)-  Exposed 
15  minutes.  Little  if  any  reaction.  Microscopic  examination  (6 
days):  Cornea,  iris,  and  lens  epithelium  unaffected.  Retina  shows 
heat  effect  involving  pigment  epithelium  only. 

Experiment  58.  Pigmented  eye.  Flint  glass  screen  (315juju).  Ex- 
posed 1  hour.  No  reaction.  Microscopic  examination  (6  days) :  Cor- 
nea, iris,  and  lens  epithelium  unaffected.  Retina  shows  burned  spot. 

Experiment  59.  Albino.  Flint  screen  (335  juju).  Exposed  lj 
hours  with  5  minutes  intermission  at  end  of  30  minutes.  No  reaction. 
Microscopic  examination  (2  days) :  Cornea,  iris,  and  lens  epithelium 
unaffected.  Retina  and  chorioid  show  burned  area. 


MAGNETITE  ARC.      QUARTZ  DOUBLE  LENS  SYSTEM.      WATER  CELL.      NO 

SCREEN. 

Experiment  60.     Exposed  5  seconds.     No  effect. 

Experiment  61.  Exposed  10  seconds.  Slight  reaction.  Corneal 
epithelium  lost  in  exposed  area. 

Experiment  62.  Exposed  10  seconds.  Result  same  as  in  Experi- 
ment 61. 

Experiment  63.  Exposed  30  seconds.  Marked  reaction.  Slight 
haze  of  cornea  with  loss  of  epithelium. 

Experiment  64.  Exposed  5  minutes.  Marked  reaction.  Soften- 
ing of  corneal  stroma.  Translucent  corneal  scar  at  end  of  two  months. 


EFFECTS   OF   RADIANT    ENERGY   ON   THE   EYE.  655 

In  the  following  experiments  (see  page  668)  the  exposure  was 
sufficient  to  produce  marked  photophthalmia  with  loss  of  corneal 
epithelium  and  endothelium,  destruction  of  corneal  corpuscles,  soften- 
ing and  swelling  of  the  stroma,  and  marked  changes  in  the  lens  epi- 
thelium. The  retina  was  normal  in  all. 

Experiment  65.     Exposed  6  minutes.    Enucleation  at  end  of  4  days. 

Experiment  66.  Exposed  20  minutes.  Enucleation  at  end  of  10 
hours. 

Experiment  67.  (PI.  2,  Fig.  6).  Exposed  20  minutes.  Enucleation 
at  end  of  48  hours. 

Experiment  68.  Exposed  20  minutes.  Enucleation  at  end  of  4 
days. 

Experiment  69.  (PI.  1,  Fig.  1).  Exposed  20  minutes.  Enucleation 
at  end  of  12  days. 

Experiment  70.  (PI.  3,  Fig.  7).  Exposed  20  minutes.  Enucleation 
at  end  of  2  months. 


MAGNETITE   ARC.      QUARTZ   DOUBLE   LENS   SYSTEM.      WATER   CELL. 

With  crown  screen  (295  WJL)  : 

Experiment  71.  Exposed  2  minutes.  Slight  conjunctival  reaction. 
Corneal  reflex  impaired  but  epithelium  intact. 

Experiment  72.  Exposed  3  minutes.  Loss  of  corneal  epithelium 
in  exposed  area. 

In  the  following  experiments  there  was  marked  keratitis  and  abiotic 
changes  in  the  lens  epithelium.  The  retina  was  normal. 

Experiment  73.  Exposed  5  minutes.  Enucleation  at  end  of  48 
hours. 

Experiment  74.  Exposed  20  minutes.  Enucleation  at  end  of  5 
days. 

Experiment  75.  Exposed  20  minutes.  Enucleation  at  end  of  10 
days. 

Experiment  76.  Exposed  20  minutes.  Enucleation  at  end  of 
34  days. 

With  .001  auramine  0  solution  in  quartz  cell  5  cm.  thick  (substituted 
for  water  cell),  and  blue  uviol  screen,  the  two  together  obstructing 
all  waves  less  than  250  w  and  longer  than  470  //ju  in  length  (see 
PI.  5). 

Experiment  77.     Exposed  45  minutes.     Enucleation  at  end  of  3 


656  VERHOEFF  AND   BELL. 

days.  Marked  keratitis  and  abiotic  changes  in  lens  epithelium. 
Retina  normal. 

With  flint  glass  screen  (298  MM)  • 

Experiment  78.  (PL  4,  Fig.  11).  Exposed  1  hour.  After  20 
minutes:  Cornea  shows  well  marked  central  haze  (heat  effect). 
Epithelium  intact.  After  24  hours:  Slight  conjunct! val  reaction. 
Haze  of  cornea  greater.  Central  loss  of  epithelium  (5  mm.).  After 
72  hours:  Corneal  epithelium  reformed.  Haze  of  stroma  persists. 
Enucleation.  Eye  immediately  opened.  Fundus  bisected  vertically. 
One  half  fixed  in  saturated  solution  of  mercuric  chloride.  The  other 
stained  by  the  vital  methylene  blue  method.  Lens  fixed  in  Zenker's 
fluid.  Microscopic  examination :  Corneal  stroma  swollen  to  |  normal 
thickness.  Corneal  corpuscles  completely  destroyed  in  posterior 
two-thirds,  present,  but  show  characteristic  abiotic  changes  in  anterior 
third.  Endothelium  necrotic  and  absent  in  places.  Lens  epithelium 
shows  marked  abiotic  changes.  Retina  normal. 

With  crown  glass  screen  (300  MM)  : 

Experiment  79.  Exposed  1  hour.  Slight  conjunctival  reaction. 
Marked  central  haze  of  cornea  with  loss  of  epithelium.  Microscopic 
examination  (48  hrs.):  Corneal  stroma  swollen  to  twice  normal  thick- 
ness. Epithelium,  corneal  corpuscles,  and  endothelium  completely 
destroyed  in  central  area.  Towards  the  periphery  corpuscles  first 
show  abiotic  changes  then  proliferative  changes  (heat  effect).  Lens 
epithelium  shows  slight  but  definite  abiotic  changes  —  swelling  of 
cells  and  characteristic  granules.  Iris  normal  (unexposed).  Retina 
normal. 

Experiment  80.  Exposed  20  minutes.  Slight  central  haze  of  cornea 
persisting  over  9  days.  Epithelium  intact. 

With  flint  glass  screen  (305  MM)  • 

Experiment  81.  (PI.  1,  Fig.  2).  Exposed  1  hour.  Immedi- 
ately after  exposure;  cornea  perfectly  clear.  After  one  hour :  Cornea 
shows  distinct  central  haze.  After  24  hours:  Cornea  more  hazy, 
epithelium  intact  and  normal.  After  3  days:  Haze  of  cornea  persists. 
There  has  been  no  loss  of  epithelium  on  daily  examination.  Micro- 
scopic examination  (3  days):  Corneal  epithelium  intact.  Stroma 
swollen  to  §  normal  thickness.  Endothelium  absent.  Corpuscles 
invisible  in  posterior  j  of  exposed  area,  present  and  actively  proliferat- 
ing in  anterior  portion.  No  evidences  of  abiotic  action.  (Iris  not 
exposed).  Lens  epithelium  normal.  Retina  normal. 

Experiment  82.  Exposed  1^  hours.  Immediately  after  exposure: 
cornea  shows  faint  haze.  After  45  minutes:  Corneal  haze  more 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          657 

distinct.  After  1  hour:  Haze  more  distinct.  Epithelium  intact. 
After  2  hours.  Epithelium  intact.  Slight  diffuse  deep  staining  of 
stroma  with  fluorescine.  Animal  avoids  obstacles  by  sight  (other 
eye  absent).  After  24  hours:  Cornea  hazy,  shows  loss  of  epithelium 
(3  mm.).  After  48  hours:  Epithelium  reformed.  Microscopic  ex- 
amination (48  hrs.);  Corneal  epithelium  intact  but  thin.  Stroma 
swollen  to  almost  twice  normal  thickness.  Corpuscles  completely 
destroyed  in  posterior  portion  of  exposed  area,  a  few  present  in  anterior 
portion  show  no  abiotic  changes.  At  periphery  of  exposed  area  the 
cells  are  actively  proliferating.  Endothelium  absent.  (Iris  not  ex- 
posed). Lens  epithelium  normal.  Retina  normal. 

Experiment  83.  Pigmented  eye.  Light  focussed  on  anterior 
pole  of  lens  instead  of  on  cornea  as  in  previous  experiment.  Pupil 
not  fully  dilated.  Total  exposure  1|  hours.  Exposed  30  minutes. 
During  the  exposure,  the  pupil  became  contracted.  Immediately 
after  exposure:  Cornea  clear.  After  50  minutes:  Cornea  shows  dis- 
tinct haze.  After  1  hour:  Exposed  1  hour.  Immediately  after 
exposure:  Iris  congested,  pupil  contracted  (about  1|  mm.)  and  irregu- 
lar, does  not  dilate  in  the  dark.  Cornea  more  hazy.  After  2  hours. 
Corneal  haze  very  marked.  Epithelium  intact,  does  not  stain.  Pupil 
slightly  larger.  After  24  hours:  No  conjunctival  reaction.  Pupil 
dilated,  but  not  fully  so.  Cornea  shows  marked  haze  without  loss 
of  epithelium.  After  48  hours :  Conditions  about  the  same.  Epithe- 
lium intact,  does  not  stain.  Microscopic  examination:  (48  hrs.): 
Corneal  epithelium  intact.  Stroma  swollen  to  f  normal  thickness, 
and  corpuscles  affected  as  in  previous  experiment.  Endothelium 
absent.  Iris  normal.  Retina  normal.  Lens  epithelium  shows  slight 
but  definite  abiotic  changes.  Cells  are  slightly  swollen  in  exposed 
area  and  a  few  of  them  contain  characteristic  granules. 

With  flint  glass  screen  (310  ^u) : 

Experiment  84.  Exposed  1|  hours.  After  24  hours:  Marked 
central  haze  of  cornea.  Epithelium  intact,  does  not  stain.  After 
2  days :  Haze  of  cornea  about  the  same.  Epithelium  intact,  does  not 
stain.  After  4  days:  Cornea  clearer.  Epithelium  intact.  Micro- 
scopic examination  (4  days):  Epithelium  intact.  Corneal  stroma 
swollen  to  about  f  normal  thickness.  Corneal  corpuscles  nowhere 
destroyed,  show  marked  proliferative  changes,  especially  in  posterior 
portion  of  cornea.  No  abiotic  changes  seen.  Endothelium  absent 
in  places.  Lens  epithelium  normal.  Retina  normal. 

With  flint  glass  screen  (315  /z/z) : 

Experiment  85.     Exposed  1§  hours.     After  24-48  hours:    No  re- 


658  VERHOEFF  AND   BELL. 

action.  Cornea  clear.  Microscopic  examination  (48  hrs.):  Cornea, 
lens  epithelium,  and  retina  normal. 

With  1.5%  copper  chloride  solution  substituted  for  water  in  quartz  cell, 
crown  glass  screen  (295  nfi)  and  blue  uviol  screen,  the  whole  obstructing 
all  waves  less  than  320  w  and  longer  than  700  H/JL  in  length. 

Experiment  86.  Exposed  1  hour.  No  effect.  Microscopic  exam- 
ination (48  hrs.):  Cornea,  lens  epithelium  and  retina  normal. 

With  1.5%  copper  chloride  solution  and  blue  uviol  screen,  obstructing 
all  waves  less  than  320  /xju  and  longer  than  700  H/JL  in  length: 

Experiment  87.  Exposed  1  hour.  No  effect.  Microscopic  exami- 
nation (3  days):  Cornea,  lens  epithelium, -and  retina,  normal. 

With  flint  glass  screen  (315 /xju).  (The  water  cell  leaked  so  that  for 
an  unknown  length  of  time  the  eye  received  also  infra  red  rays) : 

Experiment  88.  (PL  1,  Fig.  3).  Albino.  Exposed  1  hour. 
After  24  hours:  No  conjunctivitis.  Marked  haze  of  cornea,  epithe- 
lium intact.  After  48  hours:  Haze  persists.  Epithelium  intact. 
Microscopic  examination  (48  hrs.):  Corneal  epithelium  intact. 
Stroma  swollen  to  double  normal  thickness,  stains  faintly  in  eosin. 
Corpuscles  and  endothelium  completely  destroyed  in  exposed  area. 
At  periphery  of  affected  area  corpuscles  show  active  proliferation  with 
mitoses  (page  693).  Iris  shows  a  few  minute  hemorrhages  near 
pupil.  Lens  epithelium  normal.  Retina:  Pigment  epithelium  shows 
distinct  heat  effect  over  an  area  6  mm.  in  diameter.  The  cells  are 
swollen  or  stain  deeply  in  eosin,  and  their  nuclei  are  often  pycknotic. 
Otherwise  the  retina  is  normal. 

With  crown  glass  screen  (295  nn) : 

Experiment  89.  Aphakic  eye.  Pigmented.  Exposed  35  minutes 
with  intermissions  of  1  minute  every  five  minutes.  Light  focussed 
on  opening  in  lens  capsule.  After  24^18  hours:  Marked  keratitis 
with  loss  of  epithelium.  Microscopic  examination  (48  hrs.):  Cornea 
shows  typical  abiotic  changes.  Epithelium  and  endothelium  absent. 
Iris  (only  slightly  exposed)  shows  a  few  minute  hemorrhages.  Pig- 
ment epithelium  of  retina  shows  marked  heat  effect  over  an  area  4  mm. 
in  diameter.  Ganglion  cells  and  other  retinal  elements  normal. 

With  flint  glass  screen  (315  nn}  but  without  water  cell: 

Experiment  90.  Pigmented  eye.  Atropine  mydriasis.  Exposed 
30  minutes.  Immediately  after  exposure:  Cornea  clear.  Pupil  con- 
tracted. After  20  minutes:  Distinct  haze  of  cornea.  No  conjuncti- 
vitis. After  4  hours:  Haze  of  cornea  marked.  Epithelium  intact, 
does  not  stain.  No  conjunctivitis.  Pupil  larger,  vertically  oval. 
Prompt  lid  reflex  to  light.  After  24  hours:  No  conjunctivitis. 


EFFECTS   OF   RADIANT    ENERGY   ON   THE    EYE.  ()59 

Marked  haze  of  cornea.  Epithelium  intact.  Pupil  widely  dilated. 
After  48  hours :  Condition  about  the  same.  Microscopic  examination 
(48  hrs.) :  Corneal  stroma  swollen  to  f  normal  thickness.  Epithelium 
intact.  Corneal  corpuscles  completely  invisible  in  central  portion  of 
exposed  area.  At  the  periphery  of  the  latter  they  show  active  pro- 
liferation many  of  them  being  in  mitosis.  Endothelium  absent 
beneath  exposed  area.  Iris  and  lens  epithelium  normal.  Retina 
normal  —  pigment  epithelium  unaffected. 

With  flint  glass  screen  (335  MM)>  but  without  water  cell. 

Experiment  91.  Pigmented  eye.  Exposed  30  minutes.  After 
24-48  hours:  No  reaction,  cornea  clear.  Microscopic  examination 
(48  hrs.) :  Cornea,  lens  epithelium,  and  retina  normal.  Pigment  epi- 
thelium of  retina  normal. 


SUNLIGHT.      BLUE  UVIOL  SCREEN  AND  .001%  SOLUTION  OF  AURAMIN  O 
IN    QUARTZ    CELL   5    CM.    THICK. 

Light  focussed  on  cornea  by  large  quartz  lens  12  cm.  in  diameter 
and  25  cm.  in  focal  length.  Atmosphere  not  perfectly  clear  (April  2, 
1913): 

Experiment  92.  Albino.  Exposed  45  minutes.  After  24  hours: 
Very  slight  conjunct! val  reaction.  Cornea  hazy,  epithelium  intact. 
Iris  congested.  After  48  hours :  Condition  about  the  same.  Corneal 
epithelium  intact.  Microscopic  examination  (48  hrs.) :  Corneal  epi- 
thelium intact.  Stroma  swollen  to  about  f  normal  thickness.  Cor- 
puscles and  endothelium  completely  destroyed  in  exposed  area.  At 
periphery  corpuscles  show  proliferative  changes.  Affected  area  wider 
posteriorly  than  anteriorly.  No  characteristic  abiotic  changes  made 
out.  Iris  normal.  Retina  congenitally  defective  (coloboma  of  optic 
disc,  ganglion  cells  few  in  number)  shows  no  abiotic  or  heat  effects. 
Pigment  epithelium  normal. 


MAGNETITE  ARC.       QUARTZ  SINGLE  LENS.       WATER  CELL.       CROWN  GLASS 

SCREEN    (295  HfJ.). 

Experiment  93.  Right  eye  exposed  8  minutes.  Left  eye  exposed 
4  minutes.  One  hour  later;  Left  eye  exposed  4  minutes.  After 
twenty-four  hours :  Slight  reaction  in  each  eye  without  loss  of  epithe- 
lium. After  3  days:  No  reaction.  Magnetite  arc.  Double  lens 
system.  Water  cell.  Crown  screen  (295  MM)-  Exposed  left  eye 


660  VERHOEFF  AND   BELL. 

3  minutes.  After  1^  hours:  Exposed  right  eye  6  minutes;  left  eye, 
3  minutes.  Marked  reaction  with  haze  of  cornea  and  loss  of  epithe- 
lium in  each  eye.  Microscopic  examination :  (5  days  after  first  expo- 
sures) :  Cornea  of  each  eye  shows  marked  abiotic  changes  with  loss 
of  epithelium  and  endothelium.  Lens  epithelium  shows  abiotic 
changes  in  both  eyes,  but  more  marked  in  left  eye. 


HlSTOLOGICAL  TECHNIQUE. 

Fixation:  In  a  few  of  the  earlier  experiments  the  eyes  were  fixed 
in  a  warm  saturated  mercuric  chloride  solution  as  recommended  by 
Birch-Hirschfeld.  This  was  not  found,  however,  superior  to  Zenker's 
fluid  for  demonstrating  the  structure  of  the  ganglion  cells,  particularly 
the  Nissl  bodies,  and  Zenker's  fluid  at  room  temperature  was  there- 
fore used  for  fixation  in  all  except  one  of  the  experiments  relating  to 
the  retina.  Before  opening  the  eye  it  was  usually  placed  in  the 
fixing  fluid  for  about  ten  minutes.  This  prevented  the  cornea  from 
losing  its  shape  and  the  sclera  and  retina  from  becoming  distorted 
as  happened  when  the  eye  was  immediately  opened.  The  eye  was  then 
incised  all  around  at  the  or  a  serrata,  the  vitreous  body  gently  lifted 
out,  the  lens  removed  and  the  two  portions  replaced  in  the  Zenker's 
fluid  for  four  to  six  hours.  Longer  fixation  gives  less  brilliant  results. 
After  fixation  the  tissues  were  washed  in  running  water  twenty-four 
hours. 

Embedding:  Celloidin  embedding  was  employed  in  all  except  one 
experiment  in  order  to  avoid  the  shrinkage  that  results  from  the 
paraffine  process. 

Cornea  and  Iris:  Meridional  sections  8  to  10  jit  in  thickness  were 
always  made,  passing  through  the  middle  of  the  most  affected  part 
of  the  cornea  and  the  centre  of  the  pupil.  Tangential  sections  of  the 
cornea  6  to  8  n  in  thickness  were  also  frequently  made.  The  sections 
were  stained  in  alum  hematoxylin  followed  by  .2%  solution  of  water 
soluble  eosin  in  80%  alcohol. 

Lens  Capsule:  The  most  satisfactory  method  of  demonstrating 
changes  in  the  capsular  epithelium  is  by  means  of  flat  preparations. 
This  method  was  used  by  Hess  179  and  later  by  Martin,238  but  Birch- 
Hirschfeld  37  speaks  of  using  flat  sections.  The  method  as  we  have 
carried  it  out  is  as  follows :  The  eye  is  opened  as  already  described,  by 
an  incision  passing  just  behind  the  ciliary  body  all  around.  The 
zonule  is  then  cut  all  around  by  means  of  scissors,  care  being  taken 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         661 

not  to  rupture  the  capsule,  and  the  lens  removed  and  placed  in  Zenker's 
fluid  for  two  hours.  The  lens  may  be  fixed  in  situ  and  removed  after- 
wards, but  this  causes  the  iris  epithelium  to  adhere  to  it.  Birch- 
Hirschfeld  mistakenly  regarded  such  adhesions,  which  he  found  in 
the  exposed  eyes,  as  pathological.  They  may  be  removed  by  gently 
rubbing  the  capsule  with  wet  filter  paper.  The  lens  is  now  rinsed 
in  water  and  the  capsule  incised  all  around  the  equator  with  a  sharp 
knife.  The  anterior  capsule  is  now  readily  stripped  off,  floated  in 
water  and  treated  as  follows:  Lugol's  solution  (1%)  a  few  seconds. 
Water.  95%  Alcohol  two  minutes  or  longer.  Water.  10%  aque- 
ous solution  sodium  hyposulphite  until  color  of  iodine  is  removed. 
Water.  The  capsule  will  be  found  to  curl  toward  the  cell  free  side. 
It  is  now  floated  upon  a  piece  of  paper  and  by  means  of  scissors  five  • 
radial  incisions  are  made  through  both  paper  and  capsule  reaching 
to  within  a  short  distance  of  the  centre.  It  is  then  freed  from  the 
paper  and  floated  upon  a  cover  glass  with  the  curled  edges  up,  so  that 
the  epithelium  is  in  contact  with  the  glass  and  thus  will  be  nearest 
the  lens  of  the  microscope.  The  curled  edges  are  flattened  out  by 
stroking  with  bits  of  filter  paper,  which  removes  the  excess  of  water 
and  prevents  the  edges  curling  again.  The  preparation  is  now  blotted 
firmly  with  filter  paper.  Alum  hematoxylin  until  deeply  stained. 
It  is  best  to  use  a  sharply  acting  hematoxylin  solution  and  avoid  differ- 
entiating in  acid  alcohol  as  the  latter  is  apt  to  act  unevenly.  Water. 
0.2%  solution  of  water  soluble  eosin  in  80%  alcohol,  30  minutes. 
Water.  The  preparation  is  now  thoroughly  dehydrated  in  absolute 
alcohol,  cleared  in  oil  of  origanum  followed  by  xylol,  blotted  again  if 
necessary,  and  mounted  on  a  slide  in  xylol-balsam. 

Retina:  Vertical  sections  of  the  retina  6  fj.  to  8  n  in  thickness, 
were  made  in  all  cases.  These  always  included  the  optic  disc  and  the 
area  below  it  that  had  been  exposed  to  the  light  during  the  experiment. 
This  area  contains  a  much  larger  proportion  of  ganglion  cells  than  any 
other  part  of  the  retina  and  may  be  regarded  as  analogous  to  the 
human  macula,  although  it  is  much  larger  and  less  sharply  defined. 
The  ganglion  cells  are  similar  to  those  of  the  human  macula,  but  never 
occur  in  more  than  a  single  row.  Plane  sections  of  the  retina  were  also 
often  made,  and  these  were  found  to  give  the  best  demonstration  of 
the  ganglion  cells. 

Sections  were  always  stained  in  eosin  and  thionin,  which  is  proba- 
bly the  most  satisfactory  method  for  demonstrating  Nissl  bodies 
and  at  the  same  time  gives  a  beautiful  general  stain  of  the  retina. 
Dilute  aqueous  solutions  of  thionin  rapidly  lose  in  staining  power,  so 
that  it  is  important  that  they  be  always  freshly  prepared.  The  fol- 


662  VERHOEFF  AND  BELL. 

•lowing  carbol-thionin  solution  devised  by  one  of  us  retains  its  prop- 
erties indefinitely  and  from  it  a  powerful  staining  solution  may  be 
made  at  once  by  the  simple  addition  of  water: 

Thionin  to  saturation,  about     .  3  gm. 
Absolute  alcohol,  60  cc. 

Phenol  crystals  (melted)  30  cc. 

For  use,  add  one  full  drop  of  this  solution  to  2  cc.  of  distilled  water. 
Sections  are  stained  as  follows : 

(1)  Lugol's  solution  1:2:100,   1  minute,  followed  by  water,  95% 
alcohol  and  sodium  hyposulphite  solution,  to  remove  mercurial 
precipitates.     Water. 

(2)  0.2%  solution  of  water  soluble  eosin  in  80%  alcohol,  5  minutes. 
Water. 

(3)  Carbol  thionin  diluted  immediately  before  use  as  above,  5  min- 
utes.    Water. 

•(4)  Differentiate  and  dehydrate  in  95%  alcohol,  two  changes,  until 
excess  of  thionin  is  removed  and  sections  show  well  marked 
eosin  stain,  about  30  seconds. 

{5)     Oil  of  origanum. 

•(6)     Place  on  slide,  blot,  wash  in  xylol,  blot,  xylol-balsam. 

To  obtain  the  most  brilliant  results  it  is  important  not  to  overstain 
the  sections  in  thionin  solution  as  it  is  then  impossible  to  produce 
sharp  differentiation  of  the  Nissl  bodies  by  treating  with  alcohol. 
The  results  also  are  more  brilliant  the  shorter  the  time  that  has 
elapsed  between  the  fixation  of  the  tissues  and  the  staining  of  the 
sections. 

THE  CHARACTER  OF  THE  REACTIONS  OF  THE  OCULAR  TISSUES  TO 
ABIOTIC  RADIATIONS. 

CONJUNCTIVA  AND  CORNEA. 

Clinical:  Our  experiments  show  that  the  effects  on  the  conjunctiva 
and  cornea  of  moderate  exposures  to  waves  less  than  295  /j,fj,  in  length 
do  not  differ  qualitatively  in  their  clinical  aspects  from  those  produced 
by  longer  exposures  to  waves  from  295  nfj.  to  305  MJU  in  length.  Severe 
exposures,  however,  produce  markedly  different  effects  on  the  cornea 
in  the  case  of  the  short  waves  than  in  the  case  of  the  longer  waves, 
owing  to  the  fact  that  the  latter  are  not  fully  absorbed  by  the  corneal 
•stroma.  The  effects  of  severe  exposures  to  very  short  waves  is  there- 


EFFECTS   OF   RADIANT   ENERGY   ON   THE   EYE.  663 

fore  not  included  in  the  following  description,  but  will  be  given  sepa- 
rate consideration.  A  description  of  combined  thermic  and  abiotic 
effects  on  the  cornea  in  certain  experiments,  resulting  from  prolonged 
intense  exposures  is  given  on  page  694. 

After  exposure  of  a  rabbit's  eye  to  light  containing  abiotic  rays, 
no  immediate  changes  take  place,  however  great  the  intensity,  pro- 
vided a  heat  effect  is  not  produced,  and  symptoms  of  irritation  do 
not  usually  appear  for  several  hours.  In  other  words,  there  is  a  latent 
period  before  any  visible  effects  are  produced.  This  exists  not  only 
as  regards  clinical  symptoms  but  also  as  regards  histological  changes. 
In  a  general  way  it  varies  inversely  as  the  severity  of  the  exposure, 
but  in  no  case  is  the  first  appearance  of  symptoms  delayed  longer 
than  twenty-four  hours.  That  is  to  say,  a  latency  longer  than  this 
corresponds  to  an  exposure  too  slight  to  produce  any  demonstrable 
effects.  The  shortest  latent  period  observed  by  us  was  thirty  min- 
utes. This  occurred  after  intense  exposure  to  the  short  waves  of  the 
'magnetite  arc,  as  described  later.  The  least  effect  that  occurs  after 
exposure  to  abiotic  radiation  consists  in  slight  hyperemia  of  the 
conjunctiva.  After  more  intense  exposures  the  congestion  is  corre- 
spondingly greater  and  is  associated  with  edema  and  purulent  exuda- 
tion. There  also  may  be  conjunctival  ecchymoses.  The  cornea, 
after  exposures  sufficient  to  produce  slight  conjunctivitis,  remains 
clear  and  shows  only  slight  stippling  of  the  surface.  After  longer 
exposures  the  cornea  becomes  hazy  in  a  rather  sharply  defined  central 
area.  This  delimitation  is  no  doubt  due  chiefly  to  the  fact  that  the 
rays  strike  the  periphery  of  the  cornea  obliquely  so  that  there  is  less 
light  here  per  unit  area,  and  to  a  less  extent  to  the  greater  loss  by 
reflection  at  the  periphery  (see  diagram,  page  634).  Over  the  central 
area  the  epithelium  shows  marked  stippling  and  is  then  cast  off, 
usually,  however,  not  until  about  24  hours.  The  loss  of  epithelium 
sometimes  cannot  be  determined  without  the  use  of  fluorescine  stain- 
ing, owing  to  the  margins  of  the  defect  not  then  being  sharply  defined. 
This  is  due  to  the  fact  as  shown  by  microscopic  examination,  that  the 
epithelium  usually  becomes  thinned  by  desquamation  before  solution 
of  continuity  occurs.*  The  haziness  of  the  cornea  usually  reaches  its 

*  The  cornea  of  a  rabbit's  normal  eye  often  shows  punctate  spots  and  irregu- 
lar lines  after  staining  with  fluorescine  that  closely  resemble  the  lesions  of 
dendritic  keratitis.  These  are  due  to  defects  in  the  epithelium  so  small  that 
they  do  not  easily  become  visible  until  the  stain  has  diffused  through  them  into 
the  corneal  stroma,  which  requires  one  or  two  minutes.  They  are  possibly 
due  to  the  infrequent  winking  for  which  rabbits  are  noted.  They  cannot  be 
mistaken  by  anyone  familiar  with  their  appearance  for  erosions  due  to  ex- 
posure to  abiotic  radiations,  because  the  latter  stain  almost  instantaneously 
and  are  much  larger  and  sharply  defined. 


664  VERHOEFF   AND    BELL. 

maximum  in  about  48  hours,  when,  as  will  be  pointed  out,  there  is 
some  leucocytic  infiltration. 

After  3  days  the  purulent  conjunctival  discharge  becomes  less, 
but  it  may  not  entirely  subside  for  about  9  days.  The  corneal  epi- 
thelium is  usually  reformed  on  about  the  4th  day.  Haziness  of  the 
cornea  noticeably  begins  to  subside  in  3  to  10  days.  After  five  weeks 
only  a  slight  central  haze  remains.  Following  sufficiently  intense 
exposures,  new  vessels  are  seen  extending  into  the  cornea  from  the 
limbus  in  about  six  days. 

The  conjunctival  reaction  that  occurs  after  moderate  exposure 
to  abiotic  radiations,  is  only  in  very  small  part  reflexly  due  to  irrita- 
tion of  the  cornea.  This  is  proved  by  several  experiments  in  which 
the  cornea  was  exposed  through  a  diaphragm  which  protected  the 
conjunctiva.  Here,  although  the  cornea  was  markedly  affected,  and 
the  epithelium  destroyed,  the  conjunctiva  showed  no  reaction  until 
after  about  48  hours,  and  then  only  slight  hyperemia. 

The  foregoing  description  applies  to  the  effect  produced  on  the 
cornea  by  moderate  exposures  to  the  bare  mercury  vapor  quartz 
lamp,  or  bare  magnetite  arc,  and  by  relatively  long  exposures  (5  to 
20  minutes)  to  the  magnetite  arc  through  a  water  cell,  quartz  lens 
system,  and  crown  screen.  The  latter  absorbs  all  rays  less  than 
295  nn  in  length  and  thus  protects  the  corneal  stroma  from  injury. 
With  the  magnetite  arc,  and  quartz  lens  system,  but  without 
any  screen,  a  very  much  greater  as  well  as  different  effect  may  be 
produced.  With  this  arrangement  and  an  exposure  of  20  minutes  a 
dosage  is  obtained  that  is  more  than  one  hundred  and  fifty  times  as 
great  as  that  of  a  liminal  exposure  necessary  to  produce  slight  keratitis. 
Following  such  an  exposure  the  following  changes  occur.  Immediately 
after  the  exposure  the  cornea  is  perfectly  clear.  At  the  end  of  thirty 
minutes  there  is  slight  hyperemia  of  the  conjunctiva  and  central 
haziness  of  the  cornea.  At  the  end  of  four  hours  the  conjunctivitis 
is  marked  and  the  corneal  haze  much  greater.  The  exposed  area  is 
completely  anaesthetic.  The  epithelium  is  intact,  but  stains  slightly 
in  flourescine.  The  iris  is  highly  congested.  At  the  end  of  twenty- 
four  hours  there  is  a  marked  general  inflammatory  reaction  of  the 
conjunctiva  with  oedema  and  purulent  discharge.  The  epithelium 
is  lost  from  the  exposed  area  in  twenty-four  hours,  and  reformed 
about  thirty-six  hours  later.  On  the  fourth  or  fifth  day  the  cornea, 
without  becoming  more  hazy,  begins  to  swell  in  the  exposed  region. 
This  swelling  increases  and  the  affected  area  becomes  softened  until 
an  appearance  is  produced  on  about  the  eighth  day  of  a  large  flaccid 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          665 

vesicle  involving  two-thirds  the  area  of  the  cornea.  This  condition 
remains  almost  unchanged  until  about  the  thirteenth  day,  except  that 
on  about  the  sixth  day  vascularization  of  the  cornea  is  observed. 
On  about  the  fourteenth  day  the  inflammatory  reaction,  which  has 
almost  completely  subsided,  begins  again.  This  is  probably  a  reaction 
of  repair.  During  this  time  the  process  of  vascularization  makes 
rapid  progress  and  the  new  vessels  invade  the  central  area  which  is 
now  somewhat  firmer,  but  still  pits  when  touched  by  a  probe.  On  the 
twenty-fifth  day  the  inflammatory  reaction  is  again  almost  gone  and 
the  new  vessels  have  begun  to  disappear.  The  exposed  area  is  now 
only  slightly  swollen  and  no  longer  pits,  but  is  very  cloudy.  On  the 
thirty-third  day  the  vessels  have  largely  disappeared.  The  exposed 
area  is  no  longer  swollen  and  presents  a  translucent  appearance. 
After  two  months  the  surface  of  the  cornea  is  smooth  and  there  is  a 
translucent  interstitial  opacity.  The  repair  of  the  injury  is  much  more 
complete  than  could  be  expected  in  the  case  of  a  human  cornea. 

After  an  exposure  of  five  minutes  i.  c.  one-fourth  the  former  dosage, 
to  the  magnetite  arc  through  the  quartz  lens  system  and  water  cell 
the  cornea  undergoes  softening  in  the  exposed  area  as  in  the  case 
of  the  longer  exposures.  The  injury,  however,  is  repaired  without 
vascularization  of  the  cornea,  leaving  a  central  translucent  scar. 


THE  HISTOLOGICAL  CHANGES  PRODUCED  IN  THE  CORNEA  BY  ABIOTIC 

RADIATIONS. 

The  histological  changes  produced  in  the  cornea  by  abiotic  radia- 
tions were  studied  chiefly  in  eyes  exposed  to  the  magnetite  arc  with 
and  without  interposition  of  quartz  lenses  and  various  screens.  Corre- 
sponding to  the  differences  in  the  clinical  effects,  different  histological 
effects  were  obtained  when  a  crown  glass  screen  was  used  than  when 
it  was  omitted.  The  chief  difference  was  that  with  the  crown  screen 
the  corneal  stroma  escaped  injury,  due  to  the  fact  that  it  was  then 
protected  from  all  waves  which  it  strongly  absorbed,  namely,  waves 
less  than  295  juju  in  length.  With  the  crown  screen,  exposures  sufficient 
to  destroy  the  epithelium  always  severely  injured  the  corneal  cor- 
puscles. Without  the  crown  screen,  on  the  other  hand,  owing  to  the 
greater  abiotic  activity  of  the  short  rays  stopped  at  the  surface  of  the 
cornea,  the  epithelium  was  destroyed  by  exposures  too  short  to  have 
any  visible  effect  on  the  corneal  corpuscles.  On  account  of  these 
differences  the  histological  effects  produced  by  the  short  waves  and 
relatively  long  waves  will  be  described  separately. 


666  VERHOEFF  AND   BELL. 


THE  HISTOLOGICAL  CHANGES  PRODUCED  IN  THE  CORNEA  BY  ABIOTIC 
WAVES  OVER  295  MM  IN  LENGTH. 

Since,  for  reasons  already  given,  the  central  portion  of  the  cornea 
under  the  usual  conditions  of  the  experiments  is  much  more  strongly 
affected  than  the  periphery,  the  various  degrees  of  injury  produced 
are  easily  made  out  by  examining  the  cornea  from  the  periphery 
towards  the  centre.  Examined  in  this  way  twenty-four  to  forty-eight 
hours  after  exposure,  it  is  found  that  the  epithelium  first  shows  spacing 
out  of  its  basal  cells,  and  then  in  addition  desquamation  of  the  super- 
ficial layers  until  finally  the  epithelium  is  more  or  less  abruptly  cast  off. 
At  the  margins  of  this  erosion  the  individual  epithelium  cells  show 
changes  similar  to  those  met  with  in  the  case  of  the  lens  capsule,  that 
is,  formation  within  the  cytoplasm  of  eosinophilic  and  basophilic 
granules.  Swelling  of  the  cells,  however,  is  not  noticeable,  possibly 
because  the  cells  are  cast  off  when  this  occurs.  The  nuclei  are  rela- 
tively little  affected,  although  some  of  them  are  pycknotic.  Mitotic 
figures  are  observed  only  in  the  apparently  normal  epithelium  at  the 
periphery  of  the  cornea. 

After  exposures  through  a  crown  screen  (295  MM)  sufficient  to  produce 
injury  to  the  lens  capsular  epithelium,  the  corneal  lamellae  show  slight 
if  any  changes;  possibly  they  stain  less  deeply  in  eosin.  The  corneal 
corpuscles,  however,  show  marked  changes.  Just  as  in  case  of  the 
lens  epithelium,  all  of  the  cells  are  not  equally  injured  and  certain 
cells  here  and  there  entirely  escape,  which  are  fewer  in  number  the 
more  severe  the  exposure.  In  the  most  exposed  region,  after  twenty- 
four  hours  many  of  the  nuclei  are  barely  or  not  at  all  visible,  while 
most  of  the  others  are  in  various  stages  of  pycknosis  and  fragmen- 
tation. The  cytoplasm  often  contains  eosinphilic  and  basophilic 
granules  similar  to  those  seen  in  the  lens  epithelium.  These  are  more 
abundant  after  twenty-four  hours  and  are  best  seen  in  thin  tangential 
sections.  The  eosinophilic  granules  are  less  readily  seen  in  the  cornea 
than  in  the  lens  epithelium,  probably  because  they  are  to  a  greater 
or  less  degree  masked  by  the  eosin  stained  stroma.  The  effect  on  the 
corneal  corpuscles  is  progressively  less  the  deeper  they  lie,  but  an 
exposure  of  five  minutes  to  the  double  lens  system  through  the  crown 
screen  (295  MM)  is  sufficient  completely  to  destroy  all  the  corpuscles 
in  the  entire  thickness  of  the  cornea  and  also  to  destroy  the  endo- 
thelium.  Polymorphonuclear  leucocytes  begin  to  invade  the  cornea 
in  about  twenty-four  hours,  reaching  their  maximum  number  in  about 


EFFECTS   OF   RADIANT   ENERGY   ON   THE   EYE.  667 

forty-eight  hours.  The  purulent  infiltration  is  greater  the  nearer 
the  exposed  area  lies  to  the  limbus,  but  is  never  sufficient  to  account 
for  more  than  a  small  part  of  the  haziness  of  the  cornea.  It  is  also 
greater  the  larger  the  area  affected  by  the  exposure. 

The  corneal  endothelium  in  the  most  exposed  region  is  entirely 
cast  off  within  twenty-four  to  forty-eight  hours.  At  the  margins  of 
the  defect  the  nuclei  show  pycknosis  and  the  cytoplasm  often  con- 
tains the  characteristic  basophilic  and  eosinophilic  granules.  These 
changes  are  also  found  after  somewhat  less  intense  exposures,  in  cells 
that  remain  adherent  in  exposed  regions. 

Repair  of  the  Corneal  Injury.  Five  days  after  exposure  the  epithe- 
lium is  usually  found  reformed  but  thin.  The  visible  corneal  corpus- 
cles are  still  further  reduced  in  number,  and  of  those  visible  many  still 
contain  eosinophilic  and  basophilic  granules.  Towards  the  periphery 
the  nuclei  are  abnormally  rich  in  chromatin  and  many  of  them  en- 
larged. Some  of  them  show  direct  division  and  budding.  Occa- 
sionally a  mitotic  figure  is  seen  here.  The  endothelium  has  not 
reformed.  In  places  on  Descemet's  membrane  there  are  eosinophilic 
and  basophilic  granules  evidently  left  by  necrotic  endothelial  cells. 

After  ten  days  the  epithelium  is  still  thin.  The  number  of  corneal 
corpuscles  in  the  exposed  area  has  slightly  increased.  The  basophilic 
granules  are  apparently  unchanged,  but  the  eosinophilic  granules  in 
some  cells  stain  less  deeply  and  in  others  have  apparently  become 
confluent  causing  the  whole  cytoplasm  to  stain  reddish.  The  nuclei 
are  rich  in  chromatin,  often  polymorphous  in  shape,  and  sometimes 
show  direct  division  and  budding.  Few  if  any  mitotic  figures  are 
seen.  The  endothelium  is  completely  reformed.  After  five  weeks 
the  cornea  presents  an  almost  normal  appearance.  The  corneal 
corpuscles  now  slightly  exceed  the  normal  number.  Many  of  the 
nuclei  are  abnormally  large  and  a  few  cells  contain  double  nuclei. 
The  cause  of  the  slight  corneal  opacity  seen  at  this  stage  during  life 
is  not  evident  from  the  microscopic  examination. 


HlSTOLOGICAL   CHANGES    PRODUCED   IN    THE    CORNEA   BY   LlGHT  RICH 

IN  ABIOTIC  WAVES  LESS  THAN  295  w  IN  LENGTH. 

With  the  bare  magnetite  arc,  to  destroy  the  epithelium  of  the  cor- 
nea requires  an  exposure  only  one-eighteenth  of  that  required  when 
a  crown  screen  (295  /*#)  is  used.  In  the  former  case  it  is  evident 


668  VERHOEFF   AND    BELL. 

therefore  that  the  effect  is  due  almost  entirely  to  waves  shorter  than 
295  fj.fj..  After  an  exposure  of  four  minutes  to  the  bare  magnetite 
arc,  at  a  distance  of  20  cm.  the  epithelium,  at  the  end  of  forty-eight 
hours,  is  entirely  lost  from  the  central  two-thirds  of  the  cornea. 
At  the  periphery  the  epithelium  shows  gradually  increasing  desquama- 
tion  of  its  cells  until  it  is  reduced  to  a  single  layer  for  a  variable  distance 
and  then  abruptly  ends.  The  cells  even  in  the  single  layer  are  appar- 
ently not  severely  injured,  and  occasionally  one  is  found  in  mitosis. 
They  do  not  contain  basophilic  and  eosinophilic  granules,  probably 
due  to  the  fact  that  the  shortest  waves  were  absorbed  by  the  super- 
ficial cells,  while  the  remaining  waves  were  not  sufficiently  intense 
at  the  periphery  of  the  cornea  to  injure  the  deeper  cells.  The  corneal 
corpuscles,  lamellae,  and  endothelium  are  normal.  There  is,  however, 
considerable  purulent  infiltration  of  the  cornea.  This  is  fully  as  great 
as  in  the  case  of  exposures  through  a  crown  screen  sufficient  to  injure 
the  corpuscles. 

Following  an  exposure  of  20  minutes  to  the  rays  of  the  magnetite 
arc  passing  through  a  water  cell  and  concentrated  by  the  quartz 
double  lens  system,  the  following  changes  are  seen:  At  the  end  of  10 
hours  the  epithelium  towards  the  periphery  of  the  exposed  area  shows 
changes  similar  to  those  seen  after  exposure  through  a  crown  screen. 
As  the  central  area  is  approached  more  marked  changes  occur;  the 
nuclei  are  seen  to  become  extremely  pycknotic  and  the  cytoplasm 
to  stain  intensely  in  eosin.  Within  the  central  area  itself  the  super- 
ficial layers  have  become  desquamated,  leaving  usually  only  the  basal 
cells,  which  now  consist  of  cylinders  deeply  stained  in  eosin  from  which 
the  nuclei  have  entirely  disappeared.  Within  the  most  exposed  area 
at  this  stage  the  corneal  corpuscles  are  still  present  in  normal  numbers. 
Their  nuclei  show  marked  pycknosis,  but  the  cytoplasm  contains  no 
granules.  Towards  the  periphery  of  the  exposed  area  a  few  corpuscles 
containing  granules  are  seen.  The  corneal  stroma  is  swollen  to  a 
third  more  than  its  normal  thickness,  and  stains  less  deeply  in  eosin. 
Unless  the  sections  are  very  thick  the  stroma  is  apt  to  fall  out  of 
them.  The  individual  lamellae  are  still  recognizable  but  are  greatly 
distorted,  due  no  doubt  to  not  holding  their  positions  in  the  cutting 
of  the  sections.  The  endothelium  is  still  adherent,  but  appears  com- 
pletely necrotic  in  the  exposed  area,  the  neuclei  being  pycknotic  and 
the  cytoplasm  staining  deeply  in  eosin. 

After  four  days  the  epithelium  is  found  to  be  reformed.  Within 
the  most  exposed  region  the  corneal  corpuscles  are  completely  invis- 
ible and  the  endothelium  is  absent.  At  the  periphery  of  the  exposed 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          669 

area,  many  of  the  nuclei  of  the  corpuscles  are  pycknotic  or  fragmented, 
and  cells  often  contain  eosinophilic  and  basophilic  granules.  Further 
away,  the  nuclei  are  enlarged  and  some  of  them  show  direct  division. 
A  few  mitotic  figures  are  also  seen.  The  stroma  in  the  exposed  area 
is  still  more  swollen,  stains  still  less  in  eosin,  and  shows  evidences 
of  injury  down  to  Descemet's  membrane.  The  individual  lamellae 
are  no  longer  recognizable  and  the  stroma  appears  as  an  almost  homo- 
geneous substance  pervaded  by  indistinct  wavy  lines.  There  is  a 
moderate  leucocytic  infiltration. 

After  twelve  days  (PI.  I,  Fig.  1)  the  stroma  is  still  more  greatly  al- 
tered. In  the  centre  of  the  exposed  area  it  has  lost  its  normal  structure 
and  has  undergone  semi-liquefaction  almost  down  to  Descemet's  mem- 
brane. This  softened  area  contains  a  large  amount  of  fibrin  and  a 
considerable  number  of  pus  cells  and  endothelial  phagocytes.  The 
leucocytes,  however,  are  too  few  in  number  to  cause  an  appearance 
in  any  way  resembling  an  abscess.  Around  the  area  of  softening 
groups  of  corneal  corpuscles  are  actively  proliferating,  forming  cells 
similar  to  fibroblasts.  The  epithelium  is  intact  although  altered  in 
appearance.  Numerous  vessels  are  making  their  way  into  the  cor- 
nea from  the  limbus.  The  endothelium  has  been  almost  completely 
reformed,  but  presents  an  abnormal  appearance  due  chiefly  to  ine- 
qualities in  the  sizes  and  shapes  of  the  cells. 

After  two  months  the  cornea  has  returned  to  its  normal  thickness. 
The  epithelium  and  endothelium  are  normal.  The  stroma  in  the 
affected  region  presents  an  abnormal  appearance,  but  less  so  than 
might  be  expected.  The  corneal  corpuscles  are  greatly  increased  in 
number  and  their  nuclei  are  abnormally  rich  in  chromatin.  The 
new  formed  corneal  lamellae  are  less  regularly  arranged  than  in  the 
normal  cornea  and  here  and  there  occur  areas  of  hyaline  tissue  that 
has  not  yet  become  definitely  laminated.  Blood  vessels  are  still 
present  but  are  small  and  few  in  number. 


THE  CONJUNCTIVA. 

The  clinical  effects  of  exposure  of  the  conjunctiva  to  abiotic  rays 
have  already  been  described.  Histologically  the  following  changes 
were  noted  in  the  bulbar  conjunctiva  24  to  48  hours  after  exposure  to 
abiotic  radiations:  Necrosis  and  desquamation  of  the  epithelium. 
Infiltration  of  the  epithelium  with  pus  cells.  Congestion,  edema, 


670  VERHOEFF  AND   BELL. 

interstitial  hemorrhages,  and  slight  purulent  infiltration  of  the  sub- 
epithelial  tissue.  Basophilic  and  eosinophilic  granules  were  not  ob- 
served in  the  epithelium,  possibly  due  to  the  fact  that  the  cells  were 
cast  off  when  this  degree  of  injury  was  reached.  These  changes  were 
obtained  after  exposure  to  the  magnetite  arc  writh  and  without  the 
single  quartz  lens.  In  the  experiments  with  the  double  lens  system 
the.  conjunctiva  was  not  exposed. 


THE  IRIS. 

Clinical.  Twenty-four  to  forty-eight  hours  after  an  exposure 
sufficient  to  injure  the  lens  epithelium,  the  pupil  becomes  contracted 
and  the  iris  shows  marked  congestion  and  minute  interstitial  hem- 
orrhages in  the  exposed  region.  The  congestion  quickly  subsides, 
but  the  hemorrhages  may  remain  visible  for  several  weeks. 

Histological.  The  iris  is  directly  affected  only  after  exposures 
sufficient  to  injure  the  lens  epithelium.  After  exposure  to  the  bare 
magnetite  arc  sufficient  to  produce  marked  conjunctivitis  and  kera- 
titis,  but  insufficient  to  produce  apparent  injury  the  lens  epithelium  or 
corneal  corpuscles,  the  anterior  chamber  may  contain  serum  and  fibrin, 
evidently  the  result  of  an  indirect  effect  on  the  iris  vessels.  After 
exposures  sufficient  to  injure  the  lens  epithelium,  there  is  seen,  in 
addition  to  congestion  and  interstitial  hemorrhages,  an  insignificant 
exudation  of  pus  cells  from  the  iris  vessels.  With  these  changes,  few 
if  any  individual  cells  of  the  iris  may  show  signs  of  injury.  After 
an  exposure  of  20  minutes  to  the  magnetite  arc  and  lens  system, 
the  albinotic  iris  in  one  experiment  (Exp.  68)  shows  marked  cell 
changes  similar  to  those  of  the  lens  capsule.  The  cells  affected  are 
the  stroma  cells,  the  endothelial  cells  of  the  vessels,  and  the  posterior 
epithelium.  From  some  of  the  blood  vessels  the  endothelium  is  com- 
pletely lost.  Thrombosis,  however,  is  not  observed.  The  character- 
istic basophilic  and  eosinophilic  granules  are  most  noticeable  in  the 
cells  of  the  posterior  epithelium,  no  doubt  due  to  the  fact  that  these 
cells  are  most  abundant.  Similar  changes  are  found  after  6  days  in 
a  lightly  pigmented  iris  (Exp.  56)  but  here  the  pigment  hides  any 
possible  change  in  the  pigment  epithelium.  In  most  of  the  experi- 
ments with  the  double  lens  system  the  pupil  was  widely  dilated  so  that 
the  iris  was  only  slightly  exposed  to  the  light. 

Posterior  synechiae  were  not  observed  in  any  of  our  experiments- 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          671 

Birch-Hirschfeld  states  that  adhesion  of  the  pigment  epithelium  to  the 
lens  occurred  after  fixation  in  some  of  his  experiments,  although  the 
light  intensities  used  were  far  less  than  those  used  by  us.  As  already 
pointed  out,  the  adhesions  noted  by  Birch-Hirschfeld  were  undoubtedly 
artefacts  due  to  the  action  of  the  fixing  fluid  alone,  since  they  occur 
in  the  case  of  normal  eyes.  In  view  of  the  numerous  control  eyes  ex- 
amined by  this  observer,  it  is  difficult  to  understand  why  he  was  not 
aware  of  this  fact. 


THE  CHARACTER  OF  THE  CHANGES  PRODUCED  IN  THE  LENS  BY  ABIOTIC 

RADIATIONS. 

The  light  intensities  and  wave  lengths  necessary  for  the  production 
of  abiotic  effects  in  the  lens  epithelium  have  already  been  given 
(page  651). 

In  none  of  our  experiments  was  an  opacity  of  the  lens  produced 
sufficient  to  be  visible  through  the  cornea.  Even  when  the  lens  was 
examined  in  air  after  its  removal  from  the  eye  it  appeared  perfectly 
clear.  If,  however,  it  was  placed  in  normal  salt  solution  it  showed 
a  delicate  haziness  in  the  pupillary  area  48  hours  after  a  severe 
exposure. 

Histological.  In  all  except  one  experiment  upon  the  lens,  the  cap- 
sule was  removed  and  examined  as  a  flat  preparation,  so  that  it  was 
impossible  to  make  a  satisfactory  examination  of  the  lens  substance. 
To  determine  the  effect  of  the  abiotic  radiations  upon  the  latter, 
the  lens  in  one  experiment  (Exp.  67)  was  fixed  in  formalin  and  hori- 
zontal sections  made  of  it.  The  magnetite  arc,  water  cell  and  system 
of  quartz  lenses  were  used  without  a  screen,  and  the  exposure  was 
20  minutes.  This  was  the  exposure  that  had  been  found  to  produce 
extreme  changes  in  the  capsular  epithelium.  The  eye  was  enucleated 
at  the  end  of  48  hours.  On  microscope  examination  the  lens  capsule 
proper  is  found  unaltered,  while  the  epithelium  shows  the  marked 
changes  described  below.  The  lens  substance  is  definitely  affected 
but  only  for  a  microscopic  depth,  the  distance  beneath  the  capsule 
by  actual  measurement  nowhere  exceeding  20  /z.  In  this  narrow 
zone  it  stains  much  more  intensely  in  eosin  than  the  rest  of  the  lens 
substance  and  is  highly  vacuolated.  Occasionally  it  contains  an  epi- 
thelial cell  which  has  evidently  been  forced  into  it. 

Lens  Capsular  Epithelium.  This  is  the  best  possible  tissue  in  which 
to  study  the  cell  changes  produced  by  abiotic  radiations  because  of 


672  VERHOEFF  AND   BELL. 

the  simplicity  of  its  structure  and  abundance  of  its  cells,  and  because, 
by  means  of  the  flat  preparations  described  (page  660)  the  whole  of 
the  exposed  area  may  be  examined  at  once.  Moreover,  the  effects 
produced  in  it  are  not  complicated  by  the  presence  of  leucocytes, 
since  these  cannot  penetrate  it.  Following  are  the  histological 
changes  produced  in  the  epithelium  by  abiotic  radiations: 

If  the  capsule  is  fixed  immediately  after  exposure,  even  if  the  latter 
has  been  prolonged,  the  cells  appear  absolutely  normal.  After 
24  hours,  changes  are  well  marked,  and  reach  their  maximum  in  from 
48  to  72  hours.  After  severe  exposures,  the  cells  may  be  so  greatly 
affected  that  many  of  them  no  longer  adhere  to  the  capsule  unless 
the  latter  is  fixed  within  24  hours.  It  is  noteworthy  that  the  cells 
in  the  exposed  area  are  not  all  affected  alike  and  one  cell,  or  group 
of  cells,  may  be  markedly  affected  while  the  neighboring  cells  are 
only  slightly  affected.  The  chief  changes  noted  consist  in  (a) 
swelling  of  the  cells,  (b)  the  appearance  of  granules  in  the  cyto- 
plasm, and  (c)  the  formation  of  a  peripheral  wall  of  cells. 

(a)  After  short  exposures  swelling  of  the  cells  may  be  almost 
the  only  change  noted.     It  is  plainly  evident  after  an  interval  of 
20  hours,  but  does  not  reach   its   maximum  until  after  48  hours. 
It  is  associated  with  increased  transparency  of  the  cytoplasm.     All 
the  cells  do  not  swell  to  an  equal  extent,  and  as  a  result  of  the 
inequalities  in  compression  the  cells  become  misshapen  in  an  irregular 

manner. 

• 

(b)  The  granules  (PI.  2,  Figs.  5  and  6)  in  the  cytoplasm  first  appear 
before  the  cells  become  much  swollen.     They  are  present  within  10 
hours  but  are  more  abundant  after  48  hours.     While  evidently  in  the 
case  of  any  individual  cell  a  greater  exposure  is  necessary  to  produce 
them  than  is  required  to  produce  swelling  alone,  a  few  cells  contain- 
ing them  may  always  be  found  if  the  epithelium  is  affected  at  all. 
The  longer  the  exposure  the  greater  the  number  of  cells  containing 
them,  and  also  the  greater  the  number  of  granules  in  each  cell,  so 
that  after  prolonged  exposures  almost  every  cell  may  contain  them. 
The  granules  are  of  two  kinds.     The  more  abundant  are  more  or  less 
strongly  eosinophilic,  usually  round  in  shape  and  varied  in  size,  the 
largest  exceeding  half  the  size  of  the  nucleus.     One  cell  may  contain 
from  one  to  over  twenty  granules.     Each  usually  appears  to  be  situ- 
ated in  a  vacuole  which  it  does  not  quite  fill,  but  this  may  be  due  to 
shrinkage  as  a  result  of  fixation.     Close  examination  shows  that  they 
have  a  reticulated  and  subgranular  structure.     The  other  granules 
are  intensely  basophilic,  and  smaller  than  the  eosinophilic  granules, 


EFFECTS   OF   RADIANT    ENERGY    ON   THE    EYE.  673 

the  largest  being  about  one-fifth  the  diameter  of  the  nucleus  and  the 
smallest  immeasurably  fine.  They  also  are  usually  round,  but  some- 
times irregular  in  shape.  Often  they  are  contained  within  the  eosin- 
ophilic  granules.  Owing  to  their  strong  basophilic  character,  the 
natural  assumption  would  be  that  they  represent  chromatin  extruded 
from  the  nuclei.  Such  an  origin  however,  cannot  actually  be  traced. 
On  the  contrary,  the  impression  is  given  that  the  cytoplasm  first 
'breaks  up  into,  or  is  transformed  into  the  eosinophilic  granules,  and 
that  the  basophilic  granules  are  formed  primarily  within  the  latter. 
After  intense  exposures,  as  will  be  pointed  out,  the  nucleus  may 
undergo  disintegration,  in  which  case  some  of  the  granules  in  the  cyto- 
plasm are  undoubtedly  nuclear  fragments. 

(c)  The  wall,  first  so  named  by  Hess,179  consists  of  a  ring  of  deeply 
staining  closely  packed  cells  at  the  periphery  of  the  exposed  area, 
that  is  in  the  position  corresponding  to  the  pupillary  margin  at  the 
time  of  the  exposure  (PI.  3,  Figs.  8  and  9).  The  cells  are  evidently  in  a 
state  of  compression  and  in  marked  cases  may  be  heaped  upon  each 
other.  The  wall  is  visible  after  19  hours  but  later  becomes  more 
evident.  The  cells  within  it  show  only  to  a  slight  extent  the  changes 
seen  in  the  central  area.  Martin  238  assumed  that  the  wall  was  due 
to  "submaximal  damage  at  the  pupillary  margin."  This,  however, 
is  certainly  not  the  case  since  submaximal  exposures  or  any  other 
exposures  do  not  give  rise  to  a  similar  condition  of  the  cells  within 
the  pupillary  area  itself.*  Hess  explained  the  wall  as  a  result  of  the 
compression  of  the  marginal  cells  by  the  sheet  of  swollen  cells  in  the 
pupillary  area.  This  explanation  seems  undoubtedly  correct.  We 
have  found  a  similar  if  not  identical  wall  four  days  after  the  injection 
of  staphylococci  into  the  anterior  chamber.  The  cells  in  the  pupillary 
area  were  swollen  but  did  not  contain  basophilic  and  eosinophilic 
granules.  We  have  found  such  a  wall  also  24  hours  after  the  injec- 
tion of  Lugol's  solution  into  the  anterior  chamber,  as  described  below 
(page  676).  As  will  also  be  pointed  out,  a  somewhat  similar  but 
yet  different  wall  may  be  produced  by  the  action  of  heat  transmitted 
by  the  iris  (page  696). 

In  spite  of  the  marked  changes  in  the  cytoplasm  of  the  exposed 
cells,  the  nuclei  remain  comparatively  normal  in  appearance  except 

*  Martin  described  in  the  capsule  of  one  rabbit  repeatedly  exposed,  a  zone 
of  proliferated  cells  which  somewhat  resembled  the  wall  of  Hess.  The  pupil- 
lary area,  however,  was  otherwise  free  from  abiotic  changes.  The  condition 
was  attributed  to  the  effects  of  abiotic  radiations,  but  in  our  opinion  was  almost 
certainly  a  congenital  malformation  such  as  we  also  have  seen. 


674  VERHOEFF  AND   BELL. 

after  the  most  intense  exposures.  Some  nuclei  show  distortion,  due 
possibly  to  the  uneven  compression  of  the  swollen  cells,  and  some  stain 
less  deeply  than  is  normal,  but  following  exposures  through  a  crown 
screen  fragmentation  is  seldom  observed.  Marked  nuclear  changes  are 
seen  after  long  exposure  to  the  magnetite  arc  through  the  double  lens 
system  without  a  screen,  but  even  then  only  relatively  few  nuclei  are 
affected.  Ten  hours  after  such  an  exposure  nuclei  here  and  there 
show  the  following  changes :  The  nucleus  becomes  transparent  and  its 
chromatin  converted  into  coarse  deeply  staining  granules  attached 
to  the  nuclear  membrane.  The  transition  of  a  normal  nucleus  into 
this  state  is  evidently  very  abrupt.  The  nucleus  then  becomes 
polymorphous  in  shape  and  undergoes  fragmentation.  Usually  the 
fragments  are  each  bordered  by  nuclear  membrane  and  contain  one 
or  more  coarse  chromatin  granules. 

Mitotic  figures  are  first  seen  after  about  48  hours  among  the 
unexposed  cells  just  outside  the  wall  where  they  occur  in  large  num- 
bers. After  5  days  they  are  greatly  diminished  in  number  here. 
After  3  days  a  few  may  also  be  found  in  the  wall  itself.  Within 
the  exposed  area  mitotic  figures  are  not  seen  until  about  the  fifth  day 
when  they  occur  in  considerable  numbers.  At  this  time  the  cells  are 
still  swollen.  The  basophilic  granules  are  little  if  any  changed  except 
possibly  they  are  more  often  irregular  in  shape,  but  the  eosinophilic 
granules  have  largely  become  confluent  and  are  apparently  under- 
going solution.  The  mitotic  figures  are  never  seen  in  cells  containing 
granules.  Many  of  the  nuclei  are  abnormally  large  and  show  early 
stages  of  direct  division  and  budding. 

At  the  end  of  ten  or  twelve  days  the  cells  have  almost  entirely  lost 
their  swollen  appearance  and  the  basophilic  and  eosinophilic  granules 
have  almost  entirely  disappeared.  The  most  striking  feature  now 
consists  in  the  inequalities  in  sizes  and  shapes  of  the  nuclei.  Most  of 
the  nuclei  are  abnormally  large;  occasionally  one  has  three  times  the 
diameter  of  a  normal  nucleus.  Some  are  abnormally  small.  Many 
of  the  nuclei  evidently  are  undergoing  direct  division,  as  all  the  stages 
in  this  process  can  be  seen,  from  a  slight  constriction  of  the  nucleus  to 
two  nuclei  connected  by  a  delicate  strand.  In  addition  to  this,  a 
process  of  budding  can  similarly  be  traced,  the  nuclei  becoming  poly- 
morphous in  shape  and  constricting  off  buds  varying  in  size  from  that 
of  a  normal  nucleolus  to  half  that  of  a  normal  nucleus.  Some  cells 
contain  as  many  as  twelve  of  these  free  buds.  The  buds  have  the 
reticulated  structure,  staining  reaction  and  general  appearance  of  the 
nucleus  proper,  and  each  most  often  contains  a  nucleolus.  Cells 


EFFECTS   OF   RADIANT   ENERGY  ON  THE   EYE.  675 

that  contain  two  nuclei  of  nearly  equal  size  always  contain  smaller 
buds  in  addition.  At  first  glance  the  nuclear  buds  may  be  mistaken 
for  persisting  basophilic  granules,  but  careful  examination  shows  that 
they  bear  no  relation  to  the  latter  either  in  appearance  or  origin. 
Few  it  any  mitotic  figures  can  now  be  seen  in  the  exposed  area  or  else- 
where. 

At  the  end  of  5  weeks  or  2  months  the  capsule  shows  about  the 
same  appearances  as  after  10  days  (PI.  3,  Fig.  7) .  There  is  perhaps  still 
greater  variation  in  the  sizes  of  the  nuclei,  and  a  greater  number  of  the 
excessively  large  ones.  The  cells  with  double  nuclei  and  nuclear  buds 
are  still  present.  In  case  of  the  extremely  severe  exposures,  a  few 
cells  are  found  still  containing  basophilic  granules  after  two  months. 


In  connection  with  the  foregoing  observations  on  the  lens  cap.su le 
several  interesting  questions  arise.  In  the  first  place  how  is  the  abun- 
dant mitotic  division  of  the  unexposed  cells  in  and  around  the  wall  to 
be  explained?  This  proliferation  is  not  due  to  minimal  exposure  to 
the  rays  for  it  does  not  occur  in  the  pupillary  area  48  hours  after 
liminal  or  subliminal  exposures.  It  is  also  not  due  to  heat  trans- 
mitted by  the  iris,  because  when  a  flint  screen  is  substituted  for  a 
crown  screen  it  does  not  occur  after  exposures  more  than  four  times 
as  long.  The  only  remaining  possibility  seems  to  be  that  it  is  due  to 
toxic  substances  diffused  from  the  injured  cells  of  the  exposed  area. 

If  this  is  the  case  why  are  not  mitotic  figures  seen  at  the  same 
time  in  the  exposed  area?  The  answer  to  this  is  probably  that  the 
cells  are  here  so  greatly  injured  that  they  cannot  respond  at  once 
to  the  irritation  of  the  toxic  substances,  which,  moreover,  may  at 
first  be  so  concentrated  as  to  inhibit  rather  than  stimulate  the  nuclei. 
This  brings  up  the  question  whether  abiotic  radiation  is  a  direct 
stimulant  or  depressant  to  mitosis.  It  certainly  is  not  a  direct  stimu- 
lant because,  as  just  stated,  after  liminal  or  subliminal  exposures 
mitosis  does  not  occur.  On  the  other  hand  it  probably  is  a  depressant 
because  following  intense  exposures  mitosis  occurs  in  the  exposed  area 
only  after  relatively  long  intervals  (four  to  five  days)  and  then  only  in 
cells  that  have  escaped  apparent  injury.  This  is  in  marked  contrast 
to  the  action  of  heat,  which,  as  will  be  shown,  produces  abundant 
mitosis  in  48  hours  and  is  evidently  an  active  stimulant  to  cell  pro- 
liferation. 

Whether  or  not  abiotic  radiation  is  a  direct  depressant  to  mitosis 


676  VERHOEFF   AND   BELL. 

it  is  certain  that  repair  of  the  injury  to  the  lens  epithelium  takes 
place  largely  without  the  aid  of  this  process.  This  is  proved  by  the 
fact  that  mitosis  does  not  occur  in  the  severely  injured  cells,  that  is 
in  the  cells  containing  granules.  Each  of  these  cells,  therefore,  if  it 
undergoes  recovery  as  usually  is  the  case,  must  do  so  without  indirect 
division.  It  is  evident  that  the  eosinophilic  and  basophilic  granules 
finally  become  dissolved  out.  The  enlargement,  direct  division,  and 
budding  of  many  of  the  nuclei  probably  represent  the  response  of 
the  latter  in  the  process  of  cell  repair.  Similar  nuclear  changes  are 
sometimes  seen  in  malignant  tumors.  The  nuclear  buds  are  still 
present  at  the  end  of  two  months  and  their  ultimate  fate  is  prob- 
lematical. 

Finally  the  question  arises  whether  or  not  the  cell  changes  de- 
scribed are  characteristic  only  of  the  action  of  abiotic  radiation.  As 
will  be  pointed  out  later,  experiments  on  the  cornea  prove  that  the 
basophilic  and  eosinophilic  granules  are  not  produced  by  heat,  and 
thus  their  occurrence  in  cells  constitutes  a  distinct  difference  between 
heat  and  abiotic  effects.  On  the  other  hand,  the  following  experi- 
ment proves  that  the  same  cell  picture  may  be  produced  by  chemical 
agents.  A  few  drops  of  Lugol's  solution  containing  25%  iodine  were 
injected  into  the  anterior  chamber  of  a  rabbit's  eye.  The  injected 
fluid  became  mostly  precipitated  so  that  its  action  on  the  lens  surface 
was  not  uniform.  On  examining  the  lens  capsule  24  hours  later 
there  were  found,  in  addition  to  more  extreme  changes,  areas  in 
which  the  cells  showed  identically  the  same  changes,  including  the 
basophilic  and  eosinophilic  granules  as  are  produced  by  the  action 
of  abiotic  radiation.  It  is  therefore  obvious  that  these  changes  are 
not  characteristic  of  abiotic  action  alone,  but  may  be  produced  by 
other  forms  of  chemical  action  as  well.  It  is  interesting  that  in  this 
experiment,  as  previously  mentioned,  a  wall  was  formed  similar  to 
that  produced  by  abiotic  rays,  evidently  due  to  the  pressure  of  the 
injured  cells  within  the  pupillary  area  on  the  peripheral  cells  which 
were  protected  from  injury  by  the  contact  of  the  iris  with  the  lens 
(PI.  3,  Fig.  10). 

The  changes  just  described  occurring  in  the  lens  capsule  after  expo- 
sure to  abiotic  rays,  are  essentially  the  same  as  those  described  by 
Hess  179  who  used  much  longer  exposures  but  a  light  source  of  much 
less  intensity  than  employed  by  us.  Hess  does  not  describe  the 
granules  in  the  cytoplasm,  although  they  are  shown  well  in  his  excel- 
lent illustrations.  He  also  does  not  describe  direct  division  and 
budding  of  the  nuclei,  although  the  latter  process  likewise  seems  to  be 


EFFECTS   OF   RADIANT   ENERGY   ON   THE   EYE.  677 

shown  in  one  of  his  illustrations.  Apparently  he  attributed  the  repair 
of  the  injury  chiefly  to  mitosis  and  not  to  recovery  of  the  injured 
individual  cells.  He  states,  however,  that  he  has  no  evidence  that 
ultra  violet  light  is  a  direct  stimulant  to  mitosis.  Widmark,4181 
strangely  enough,  found  mitotic  figures  only  in  the  exposed  area  and 
regarded  ultra  violet  light  as  a  direct  stimulant  to  cell  proliferation. 
Birch -Hirschf eld  38  states  that  by  means  of  a  20  diopter  glass  lens 
he  focussed  the  light  of  a  5  ampere  arc  light  through  a  euphos  glass 
screen  upon  the  eye  of  a  rabbit  for  five  minutes  for  three  successive 
days  and  on  the  day  after  the  last  exposure  obtained  the  changes 
described  by  Hess.  The  euphos  screen  obstructed  all  rays  less  than 
400  juju  in  length.  It  is  not  stated  that  a  water  cell  was  used,  and  the 
diameter  of  the  lens  was  not  mentioned.  In  spite  of  such  a  remarkable 
result  it  is  not  stated  that  the  experiment  was  repeated.  We  have 
been  unable  to  obtain  such  a  result  through  a  light  flint  screen  trans- 
parent for  waves  down  to  315  juyu  with  the  magnetite  arc  and  still 
greater  concentration  of  energy.  Moreover  in  an  experiment  in  which 
we  focussed  sunlight  upon  the  lens  by  means  of  a  large  mirror  no 
changes  in  the  lens  capsule  resulted  within  the  pupillary  area,  although 
there  was  complete  necrosis  of  the  iris  due  to  heat.  The  lens  capsule 
was  affected  only  beneath  the  pupillary  margin  where  it  had  been  in 
contact  with  the  heated  iris  and  even  here  the  changes  were  not  such 
as  are  produced  by  abiotic  action.  We  are  therefore  compelled  to 
believe  that  Birch-Hirschfeld  was  in  error.  Possibly  he  mistook  a 
heat  effect  similar  to  that  just  noted  for  the  changes  described  by 
Hess.  He  had  never  previously  obtained  the  latter  changes  in  any 
of  his  experiments  and  hence  from  personal  observation  was  no  doubt 
unfamiliar  with  their  appearance. 


POSSIBLE  ABIOTIC  EFFECTS  OF  RADIANT  ENERGY  ON 

THE  RETINA. 

It  might  be  supposed  that  if  a  source  of  light  is  not  sufficiently  rich 
in  abiotic  rays  to  damage  the  cornea,  the  retina  could  not  be  injured 
by  these  rays.  This,  however,  is  not  necessarily  true  because  if  the 
source  of  light  is  so  small  in  size  that  the  area  of  its  retinal  image  is 
less  than  that  of  the  pupil,  the  intensity  per  unit  area  as  concerns 
transmissible  rays  will  be  greater  on  the  retina  than  on  the  cornea. 


678  VERHOEFF  AND   BELL. 

In  fact  under  certain  conditions,  and  with  a  moderately  dilated  pupil 
the  intensity  of  the  light  reaching  the  retina  will  be  enormously 
greater  than  the  same  light  as  it  passes  through  the  cornea.  For  this 
reason  it  will  be  seen  that  if  the  transmissible  rays  were  capable  of 
injuring  tissue  cells,  the  macula  of  the  eye  might  be  seriously  damaged 
in  spite  of  the  fact  that  the  cornea  and  lens  remained  unaffected. 
This,  of  course,  actually  happens  in  eclipse  blindness  in  which,  how- 
ever, as  will  be  pointed  out,  the  effect  is  due  entirely  to  heat  generated 
in  the  pigment  epithelium. 

There  are  two  conceivable  ways,  exclusive  of  heat  effects,  in  which 
the  retina  could  be  injured  by  light.  If  the  light  were  sufficiently 
intense  it  might  overstimulate  the  physiological  mechanism  upon 
which  the  perception  of  light  is  dependent  and  thus  lead  to  more  or 
less  permanent  impairment  of  this  mechanism.  It  is  obvious  that 
such  an  effect  could  not  readily  be  produced  by  light  of  wave  lengths 
less  than  400  ju/x  since  the  latter  has  relatively  little  power  to  stimulate 
this  mechanism  even  in  aphakic  eyes.  The  other  possibility  is  that 
intense  light  might  injure  the  cells  of  the  retina  by  abiotic  action  in 
the  same  way  that  light  rays  of  short  wave  length  injure  tissue  cells 
in  general.  In  connection  with  this  possibility  two  facts  previously 
established  by  us  must  be  taken  into  consideration,  namely  that 
within  wide  limits  discontinuous  exposures  to  abiotic  rays  have  the 
same  total  effect  as  a  continuous  exposure  of  the  same  total  length, 
and  that  there  is  a  limit  below  which  such  summation  does  not  occur. 
Thus  it  would  a  priori  seem  possible  that  if  an  individual  fixed  a  bright 
source  of  light  many  times  daily,  serious  damage  to  the  macula  might 
result. 

The  problem  in  regard  to  the  retina  that  chiefly  concerns  us  in  the 
present  investigation  may  be  briefly  stated  thus:  exclusive  of  a  heat 
effect,  can  the  retina  of  the  human  eye  be  injured  by  light  of  any  or  all 
wave  lengths  that  can  possibly  reach  it  through  the  cornea  and  lens? 
In  attempting  to  answer  this  question  it  is  important  first  to  inquire 
whether  or  not  the  waves  that  are  able  to  pass  through  the  dioptric 
media  are  injurious  to  tissue  cells  in  general.  If  they  are  so  injurious 
the  question  is  obviously  to  be  answered  in  the  affirmative.  If  they 
are  not,  the  question  is  in  all  probability  to  be  answered  in  the  nega- 
tive, but  not  perhaps  with  absolute  certainty,  since  it  is  conceivable 
that  the  retinal  cells  are  more  susceptible  to  injury  by  light  than  are 
other  tissue  cells. 

It  has  been  shown  by  Hallauer  152  and  others  that  the  adult  human 
lens  always  absorbs  all  waves  less  than  376  /JL/J,  in  length,  and  usually 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         679 

all  those  less  than  400  n/j.  in  length.  Now  we  have  already  shown 
that  the  corneal  epithelium  and  lens  capsule  are  not  affected  in  the 
slightest  degree  when  exposed  one  and  one-half  hours  to  rays  as  short 
as  310  n/j.  even  when  the  intensity  is  considerably  greater  than  that  to 
which  the  retina  is  ever  subjected  in  the  case  of  any  of  the  known 
artificial  light  sources.  This  exposure  is  at  least  forty-five  times 
greater  than  that  required  to  affect  the  corneal  epithelium  by  waves 
of  295  IJL/JL  and  less.  For  the  retina  therefore  to  be  affected  by  the 
abiotic  action  of  light  transmitted  by  the  lens,  it  would  have  to  be 
many  times  more  sensitive  to  such  action  than  the  corneal  epithelium. 
There  is  no  reason  to  believe  however,  that  this  is  the  case,  but  on  the 
contrary,  since  the  abiotic  effect  depends  upon  the  amount  of  absorp- 
tion of  the  waves,  there  is  strong  reason  for  believing  that  the  corneal 
epithelium  and  retina  are  about  equally  sensitive  to  abiotic  action. 
Assuming  this  to  be  so,  these  experiments  show  conclusively  that  the 
human  eye  could  be  fixed  steadily  and  at  close  range  upon  the  magne- 
tite arc  certainly  for  over  two  hours  and  probably  for  many  hours 
without  suffering  damage  to  the  retina  from  abiotic  action.  Since 
as  already  pointed  out  the  intensity  of  the  image  of  a  source  of  light  of 
such  small  size  as  that  in  question  decreases  as  the  square  of  the  dis- 
tance, the  danger  of  injury  to  the  retina  at  ordinary  distances  would 
be  absolutely  negligible. 

In  the  case  of  the  lenses  of  some  children,  Hallauer  found  a  very 
weak  transmission  band  at  315  to  330  /i/z.  This,  however,  does  not 
invalidate  the  application  of  the  above  argument  to  the  case  of  chil- 
dren, since  we  have  shown  that  such  waves  are  without  abiotic  effect. 

While  it  seems  to  us  that  the  foregoing  facts  prove  conclusively 
enough  that  the  lens  affords  complete  protection  to  the  retina  from  the 
abiotic  action  of  light,  in  view  of  the  fact  that  Birch-Hirschfeld  claims 
to  have  produced  pathological  changes  in  the  retinae  of  normal  rab- 
bit's eyes  by  exposure  to  ultra  violet  light  (cf .  page  687),  we  have  under- 
taken to  investigate  this  question  by  direct  experiment  upon  the  retina 
itself. 

Such  an  investigation  presents  several  difficulties.  In  the  first 
place  it  is  impossible  to  reproduce  with  animals  exactly  the  conditions 
that  obtain  when  the  human  eye  is  fixed  upon  a  small  intense  source 
of  light.  This  is  so  because  it  is  impossible  to  insure  in  the  case 
of  an  animal  that  the  small  image  of  the  light  source  will  always  fall 
upon  the  same  spot  in  the  retina  during  the  exposure.  Moreover, 
even  if  this  were  possible  it  would  be  difficult  if  not  impossible  to  find 
with  certainty  such  a  small  area  on  microscopic  examination  unless 


<380  VERHOEFF  AND   BELL. 

the  lesion  produced  was  well  marked.  It  is  therefore  necessary  to 
illuminate  a  large  area  of  the  retina.  This  we  have  done  by  means  of  a 
suitable  system  of  quartz  lenses  used  in  connection  with  the  magne- 
tite arc  as  described  on  page  648.  Intense  illumination  of  such  a  large 
area,  however,  for  a  long  period  of  time  entails  a  danger  of  over- 
heating the  fundus  of  the  eye.  This  we  have  successfully  obviated 
by  interposing  a  quartz  cell  5  cm.  thick  filled  with  distilled  water  to 
absorb  most  of  the  infra  red  rays.  If  this  had  not  sufficed,  heat  effects 
could  probably  still  have  been  prevented  by  interrupting  the  expo- 
sures at  intervals  to  allow  for  cooling  to  take  place,  a  procedure  that 
no  doubt  would  be  necessary  for  light  intensities  only  slightly  greater 
than  that  used  by  us.  In  fact  in  one  of  these  experiments  in  which 
the  water  cell  leaked,  a  heat  effect  on  the  pigment  epithelium  was 
actually  noted  (Exp.  88). 

As  will  be  seen  the  system  of  quartz  lenses  employed  concentrated 
the  light  more  intensely  upon  the  cornea  and  lens  than  upon  the  retina. 
Advantage  was  therefore  taken  of  this  fact  to  determine  at  the  same 
time  the  effect  of  exposures  through  various  screens  upon  these  struc- 
tures, the  results  of  which  have  already  been  given.  None  of  the 
screens  obstructed  any  waves  longer  than  305  nfj,  to  315  nn,  that  is, 
any  waves  that  otherwise  could  have  reached  the  retina  through  the 
lens.  The  screens  also  prevented  excessive  keratitis,  which  we  de- 
sired to  avoid  since  it  would  have  prevented  us  from  later  making 
satisfactory  tests  of  the  lid  reflex  and  pupillary  reaction  to  light. 
If  these  reflexes  had  been  abolished  this  fact  alone  would  have  fur- 
nished sufficient  proof  of  the  deleterious  action  of  the  radiations  on 
the  retina.  As  a  matter  of  fact,  except  immediately  after  exposure 
a  lid  reflex  was  always  obtainable. 

The  details  of  these  experiments  are  given  on  pages  655-658. 
(Experiments  65  to  90).  It  will  be  observed  that  the  exposure  was  as 
long  as  one  and  one-half  hours  in  each  of  four  experiments  and  one 
hour  in  each  of  six  experiments.  In  all  except  one  experiment  the 
retinae  were  prepared  for  microscopic  examination  in  the  manner 
already  described  (page  661).  In  Experiment  78  the  eye  was  immedi- 
ately opened  and  the  retina  bisected  vertically  through  the  optic  disc, 
one  half  being  fixed  in  a  saturated  solution  of  mercuric  chloride  and 
embedded  in  paraffin.  The  sections,  2  p,  in  thickness,  were  stained 
in  thionin  as  in  the  case  of  the  other  experiments.  The  other  half 
of  the  retina  was  used  for  vital  methylene  blue  staining,  the  results  of 
which  will  be  mentioned  later  in  commenting  on  Birch-Hirschf eld's 
^observations  (page  687).  In  none  of  the  experiments  could  any 


EFFECTS   OF   RADIANT    ENERGY   ON   THE   EYE.  681 

apparent  changes  be  found  in  the  exposed  retinae  that  could  not  be 
found  in  unexposed  retinae  prepared  by  the  same  method.  Certainly 
if  there  were  any  differences  in  regard  to  the  Nissl  bodies  of  the  gang- 
lion cells  they  were  too  slight  to  be  of  any  pathological  significance. 

These  experiments  thus  show  that,  so  far  as  can  be  determined  by 
histological  examination,  the  retina  of  the  normal  eye,  exclusive  of 
heat  effects,  is  fully  protected  from  abiotic  action  by  the  lens.  Since 
however,  the  objection  may  be  brought  forward  that  the  retina  may  be 
injured  so  far  as  its  function  is  concerned  without  showing  any  histo- 
logical evidence  of  the  fact,  we  have  endeavored  to  exclude  this  possi- 
bility also.  For  this  purpose  we  employed  the  monkey  instead  of  the 
rabbit  because  this  animal  possesses  a  macula  similar  to  that  of  man. 
With  the  lens  system  described  it  is  easily  possible  to  illuminate 
intensely  a  sufficient  area  of  the  retina  to  insure  that  the  macula  is 
always  included.  If  under  these  circumstances  the  light  has  an 
injurious  action  on  the  retina  it  will  be  rendered  evident,  since  the 
macula  is  injured,  by  marked  impairment  in  sight  and  particularly 
by  a  loss  or  impairment  of  the  pupillary  reaction.  To  avoid  injury 
to  the  cornea  by  abiotic  rays  and  injury  to  the  retina  by  heat  we  made 
use  of  a  1|%  solution  of  copper  chloride  in  a  quartz  cell  5  cm.  thick. 
The  spectrum  of  this  solution  (PI.  5,  Fig.  4)  shows  that  it  absorbs  all 
waves  shorter  than  320 n/j.  as  well  as  all  the  so-called  heat  waves.  It 
thus  does  not  obstruct  any  short  waves  that  could  otherwise  reach  the 
retina  through  the  lens. 

In  these  experiments  two  monkeys  were  employed  in  each  of  which 
the  left  eye  was  blind.  One  was  an  old  female  monkey,  whose  left 
eye  had  been  rendered  blind  by  an  experimental  Kronlein  operation 
involving  injury  to  the  optic  nerve,  one  year  previous  to  the  first  of 
the  present  experiments.  The  other  was  a  young  full  grown  male 
monkey,  whose  left  eye  had  been  rendered  blind  by  injection  of 
alcohol  into  the  orbit  nine  months  previous  to  the  first  of  the  experi- 
ments. Ophthalmoscopic  examination  showed  complete  optic  atrophy 
in  the  left  eye  of  each.  Neither  monkey  could  find  the  way  about 
when  the,  right  eye  was  excluded  from  vision.  Direct  pupillary  re- 
action to  light  was  absent,  but  the  consensual  reaction  was  well 
marked.  This  made  it  possible  to  determine  the  presence  of  a  pupil- 
lary reaction  while  the  right  eye  was  under  the  influence  of  the  mydri- 
atic,  while  the  fact  that  the  left  eye  was  blind  made  it  easy  to  detect 
any  impairment  of  vision  of  the  right  eye.  In  each  animal  the  visual 
acuity  of  the  right  eye  was  high,  as  shown  by  the  ease  with  which  it 
was  able  to  catch  flies  and  lice.  The  absence  of  binocular  vision  did 


682  VERHOEFF  AND   BELL. 

not  seem  to  hamper  either  animal  in  its  judgment  of  distance  except 
for  a  short  time  after  the  left  eye  had  been  made  blind. 

In  all  four  experiments  the  magnetite  arc  was  used  and  the  same 
arrangement  of  lenses  employed  as  in  the  previous  experiments  with 
rabbits,  the  quartz  cell,  as  stated,  being  filled  with  a  1|%  solution  of 
copper  chloride.  The  light  was  focussed  on  the  centre  of  the  cornea. 
The  animal  was  placed  in  a  box  which  allowed  only  the  head  to 
protrude,  and  the  eyelids  kept  open  by  means  of  a  small  speculum. 
The  head  was  forcibly  held  in  position  by  the  hand  of  the  observer. 
For  the  first  five  minutes  the  animal  was  difficult  to  control,  but  after 
this  no  great  difficulty  was  experienced  in  keeping  the  eye  in  place.  No 
local  or  general  anaesthetic  was  employed.  Normal  salt  solution  was 
dropped  on  the  cornea  from  time  to  time.  The  pupil  of  the  right  eye 
was  previously  dilated  by  homatropine  except  in  the  third  experiment 
in  which  atropine  was  used. 

To  give  some  idea  of  the  light  intensity  and  duration  of  the  exposures 
in  these  experiments,  it  may  be  well  to  state  that  one  of  us  exposed 
his  eye  with  undilated  pupil  to  these  conditions  for  fifteen  seconds, 
and  obtained  an  absolute  scotoma  which  gradually  disappeared  within 
five  minutes.  Erythropsia  persisted  about  three  minutes  and  was 
followed  by  xanthopsia  which  lasted  the  remainder  of  the  five  minutes. 


EXPERIMENTS. 

Experiment  94.  March  7,  1913.  Young  monkey,  Macacus  Rhe- 
sus. Right  eye  exposed  1|  hours.  Immediately  after  exposure  there 
is  a  lid  reflex  to  a  new  2^  volt  tungsten  flash  light,  and  within 
five  minutes  the  consensual  pupillary  reaction  is  apparently  normal. 
Within  ten  minutes  the  animal  is  able  to  see  an  apple  five  feet  away, 
which  he  approaches  and  takes  from  the  hand.  March  8.  Cornea 
clear.  Consensual  pupillary  action  normal.  Slight  direct  pupillary 
reaction  in  right  eye  in  spite  of  mydriasis.  Owing  evidently  to  the 
cycloplegia,  the  animal  cannot  catch  flies  readily.  After  several  days, 
the  mydriasis  having  disappeared,  the  animal  is  able  to  catch  flies 
with  his  usual  dexterity. 

Experiment  94a.  March  28,  1913.  Old  female  monkey.  (Java.) 
Right  eye  exposed  1^  hours.  Immediately  after  exposure  the  lid  re- 
flex to  the  flash  light  is  absent,  but  is  present  in  five  minutes.  Con- 
sensual pupillary  reaction  not  determinable  owing  to  some  of  the 


EFFECTS   OF   RADIANT   ENERGY    ON    THE   EYE.  683 

mydriatic  having  accidently  gotten  into  the  left  eye.  Animal  has 
great  difficulty  in  getting  around,  vision  evidently  being  much  im- 
paired. After  one  hour  vision  is  much  improved;  the  animal  follows 
the  observer  with  the  eye.  March  29,  1913.  Cornea  clear.  Well 
marked  lid  reflex  to  flash  light.  Consensual  pupillary  reaction  also 
well  marked.  Visual  acuity  of  animal  apparently  normal  except  that 
animal  has  difficulty  in  catching  flies  owing  to  effect  of  cycloplegia. 
After  several  days,  the  mydriasis  having  disappeared,  the  animal  is 
able  to  catch  flies  with  her  usual  dexterity. 

Experiment  94b.  December  4, 1913.  Old  female  monkey.  Right 
eye  exposed  1^  hours.  One  minute  after  end  of  exposure  there  is  a 
barely  perceptible  consensual  pupillary  reaction.  After  six  minutes 
the  reaction  is  well  marked.  Animal  now  released.  Cannot  see 
approach  of  observer's  hand.  Is  compelled  to  feel  her  way  to  her 
perch  in  the  cage.  After  one  hour  she  is  still  apparently  blind;  can- 
not see  a  carrot  held  near  her,  although  she  takes  it  when  placed 
against  her  mouth.  After  seven  hours,  vision  is  still  impaired. 
December  5,  (18  hours).  Cornea  clear.  Vision  apparently  normal  — 
sees  carrot,  avoids  hand  movements  etc.,  even  in  poorly  illuminated 
cage.  Consensual  pupillary  reaction  normal.  After  the  mydriasis 
has  disappeared  the  animal  catches  flies  as  usual. 

Experiment  94c.  February  5,  1914.  Young  monkey.  Right  eye 
exposed  1^  hours.  Three  minutes  after  beginning  of  exposure  the 
consensual  pupillary  reaction,  tested  with  flash  light,  is  absent. 
Immediately  after  end  of  exposure  the  lid  reflex  to  flash  light  is  present, 
but  the  consensual  pupillary  reaction  is  absent.  At  the  end  of  three 
minutes  the  latter  is  distinctly  .visible,  and  in  six  minutes  is  well 
marked.  Animal  now  released,  finds  his  way  at  once  to  perch,  avoids 
hand  of  observer  —  evidently  sees  well.  One  hour  after  exposure 
the  eye  lids  of  right  eye  are  sewed  together.  When  released  the 
animal  cannot  find  his  way  about  and  is  easily  caught,  thus  showing 
that  if  the  sight  of  the  right  eye  had  been  affected  the  fact  would 
have  been  easily  determined.  February  6.  There  is  a  small  abra- 
sion of  the  cornea  probably  due  to  the  animal  having  frequently 
rubbed  his  eye  as  a  result  of  a  slight  irritation  produced  by  the  sutures. 
Cornea  clear.  Consensual  pupillary  reaction  intact.  Animal  sees  well. 
February  7.  The  abrasion  of  the  cornea  is  healed.  Consensual 
pupillary  reaction  intact.  Animal  shows  no  evidences  of  poor  vision. 
After  the  mydriasis  has  disappeared  the  direct  pupillary  reaction  to 
light  is  normal  and  the  animal  seems  to  have  normal  vision. 

The  results  of  these  experiments  show  that  even  with  exposures  of 


684  VERHOEFF   AND   BELL. 

extreme  intensity  and  length,  but  insufficient  to  produce  heat  effects, 
it  is  impossible  to  injure  the  retina  by  light  containing  any  or  all  rays 
capable  of  reaching  it  through  the  lens.  They  exclude  both  the  pos- 
sibility of  injuring  the  retina  by  over  stimulating  its  perceptive 
mechanism,  and  also  of  injuring  it  by  the  abiotic  action  of  light. 
Most  surprising  was  the  rapidity  with  which  the  retina  regained  its 
function.  Thus  in  all  four  experiments  within  six  minutes  the  con- 
sensual pupillary  reaction  was  fully  reestablished.  There  was  in  both 
sets  of  experiments,  however,  a  marked  difference  between  the  young 
and  the  old  monkey  in  regard  to  the  time  required  for  the  restoration 
of  useful  vision.  In  the  case  of  the  young  monkey  sufficient  vision  to 
enable  him  to  see  his  way  about,  avoid  hand  movements,  etc.,  was 
present  in  ten  minutes  after  the  exposure  ended.  The  old  monkey 
on  the  other  hand  was  practically  blind  for  an  hour  or  more.  In  fact 
her  visual  acuity  did  not  seem  to  be  fully  restored  until  the  morning 
following  the  exposure.  Both  animals  were  able  to  catch  flies  with 
their  usual  expertness  after  the  mydriasis  had  disappeared.* 

The  results  obtained  in  these  experiments  would  also  seem  to  be  of 
some  significance  in  regard  to  the  question  of  light  adaptation.  They 
suggest  that  after  a  certain  state  of  retinal  fatigue  is  reached  no 
further  effect  is  produced,  however  long  the  exposure.  In  fact  it  would 
seem,  in  young  individuals  at  least,  that  after  this  stage  is  reached  the 
recuperative  processes  begin  while  the  retina  is  still  exposed.  This 
aspect  of  the  question,  however,  does  not  concern  us  here  and  further 
experiments  would  be  necessary  to  elucidate  it  fully. 

In  addition  to  the  experiments  on  the  eyes  of  monkeys  we  have 
availed  ourselves  of  an  exceptional  opportunity  to  make  a  similar 
experiment  upon  a  human  eye.  The  subject  was  a  female  patient 
aged  50  years  affected  with  carcinoma  of  the  eyelid  and  orbit,  the 
growth  being  so  extensive  as  to  necessitate  removal  of  the  eye.  The 
left  eye  itself  was  apparently  normal,  the  media  being  clear  and  the 
fundus  normal.  The  visual  acuity  was  reduced  to  |§—  (unimproved 
by  lenses)  for  some  reason  not  definitely  determined,  but  probably 
due  to  some  irregularity  in  refraction  resulting  from  the  pressure  of 
the  upper  lid.  The  lower  lid  was  almost  completely  destroyed,  while 
the  upper  lid  was  somewhat  drawn  down  by  cicatricial  tissue  at  the 
outer  can  thus.  It  was  therefore  necessary  for  the  observer  to  hold 
up  the  eyelid  by  finger  pressure  during  the  experiment.  The  right 

*  Both  of  these  monkeys  were  later  killed,  one  after  seven  months,  the  other 
after  fourteen  months,  and  on  microscopic  examination  the  eyes  that  had 
been  exposed  were  found  normal. 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          685 

eye  was  normal  and  had  normal  visual  acuty.  Before  the  experiment 
the  pupil  of  the  left  eye  was  dilated  with  atropine,  but  the  visual 
acuity  remained  the  same.  The  total  exposure  was  less  than  in  the 
case  of  the  monkeys,  owing  to  the  patient  becoming  somewhat  fatigued, 
and  for  the  same  reason  also  the  exposure  was  not  continuous,  but 
otherwise  the  conditions  of  the  experiment  were  the  same. 

The  total  exposure  was  55  minutes,  and  the  interval  between  the 
separate  exposures  was  about  1|  minutes.  The  first  three  exposures 
were  3,  9,  12  minutes  respectively,  the  remainder  were  5  minutes  each. 
At  the  beginning  of  each  exposure  the  patient  stated  that  the  "light 
was  like  the  sun."  At  the  end  of  the  sixth  exposure  there  was  ery- 
thropsia  and  the  visual  acuity  was  reduced  to  counting  of  fingers  at 
one  foot.  Within  1\  minutes  after  the  last  exposure  the  consensual 
pupillary  reaction  was  well  marked,  and  the  patient  could  with  diffi- 
culty count  fingers  at  six  feet.  Three  minutes  after  the  last  exposure 
there  was  only  slight  erythropsia.  Xanthopsia  was  not  noted  at  any 
time  but  may  have  been  unrecognized  by  the  patient.  After  10 
minutes  the  visual  acuity  wras  ^55.  There  was  an  appearance  of  a 
mist  before  the  eye,  but  no  erythropsia.  After  l|  hours  the  visual 
acuity  was  ^,  and  a  slight  mist  still  persisted.  After  3  hours  the 
visual  acuity  was  fg+,  and  a  white  surface  seemed  almost  but  not 
quite  as  white  as  with  the  right  eye.  After  22  hours  (in  the  morning), 
the  visual  acuity  was  §§—  as  before  the  experiment.  There  was  no 
erythropsia,  and  central  color  vision  was  perfect  for  red,  blue  and 
green.  24  hours  after  the  exposure  the  eye  was  enucleated.  On 
microscopic  examination  the  cornea,  iris,  lens  epithelium  (flat  prepara- 
tion), and  retina  were  found  to  be  normal. 

The  result  of  this  experiment  confirms  those  obtained  with  the 
monkeys.  It  is  obvious  that  the  retina  could  not  have  been  injured 
by  abiotic  action  of  light,  since  the  visual  acuity  was  fully  restored 
within  3  hours  and  remained  so  the  following  morning.  The  rapid- 
ity with  which  the  erythropsia  disappeared  was  unexpected,  and 
indicates  that  duration  of  exposure  is  equally  as  important  as  its 
intensity  in  the  production  of  persistent  erythropsia. 


686  VERHOEFF  AND  BELL. 


POSSIBLE  EFFECTS  OF  ABIOTIC   RADIATIONS  ON  THE 
RETINAE  OF  APHAKIC  EYES. 

Since  it  has  been  shown  experimentally  that  abiotic  waves  may  pass 
through  the  cornea  and  injure  the  lens  epithelium,  it  would  seem  that 
exposure  of  an  aphakic  eye  to  a  light  source  rich  in  such  waves  might 
seriously  damage  the  retina.  Assuming  as  is  probable,  that  the  retina 
has  the  same  susceptibility  to  abiotic  action  of  light  as  the  lens  epi- 
thelium, the  minimal  exposure  to  the  bare  magnetite  arc  necessary  to 
injure  the  retina  of  an  aphakic  human  eye  may  be  closely  approxi- 
mated from  the  data  of  our  experiments.  The  working  diameter  of 
the  single  quartz  lens  was  4.2  cm.,  and  the  working  focal  distance  14 
cm.,  making  the  working  aperture  1/3.3  This  corresponds  to  the  aper- 
ture of  a  human  aphakic  eye  with  a  pupil  4.5  mm.  wide.  Now  we 
found  that  the  lens  epithelium  of  a  normal  rabbit's  eye  was  unaffected 
by  an  exposure  of  6  minutes  to  the  single  lens  system  through  a  crown 
screen  (295  ^n),  but  moderately  affected  by  an  exposure  of  12  minutes. 
The  liminal  exposure  may  therefore  be  taken  as  8  minutes.  The  total 
loss  by  reflection  etc.  from  the  surfaces  of  the  lenses,  screen,  and  water 
cell,  amounts  to  about  50%.  Deducting  this  percentage,  the  mini- 
mum exposure  to  the  magnetite  arc  necessary  to  affect  the  retina  of  a 
human  aphakic  eye  would  therefore  be  about  4  minutes,  providing 
that  the  eye  was  close  enough  for  the  formation  of  a  distinct  image, 
and  ignoring  the  blurring  due  to  the  lessened  refraction  of  an  aphakic 
eye.  The  absorption  of  the  cornea  is  allowed  for  in  this  calculation, 
since  in  the  experiments  the  light  passed  through  the  cornea,  but  the 
general  absorption  of  the  vitreous  humor  is  not.  Assuming  this  to 
be  about  the  same  as  that  of  the  cornea  (although  it  probably  i? 
greater)  the  calculated  exposure  would  be  increased  to  about  6  minutes. 
Since  beyond  If  meters,  owing  to  the  small  size  of  the  source,  the 
intensity  of  the  light  on  the  retina  would  diminish  as  the  square  of  the 
distance,  it  is  safe  to  say  that  under  the  most  favorable  conditions,  it 
would  require  fixation  of  the  bare  magnetite  arc  at  a  distance  of  3 
meters  for  almost  f  hour  to  injure  the  retina  of  an  aphakic  eye. 
According  to  our  experiments  on  the  effects  of  repeated  exposures 
(page  641)  a  daily  total  exposure  of  3  the  liminal,  which  in  the  present 
case  would  be  8  minutes  at  a  distance  of  3  meters  from  the  mag- 
netite arc,  would  produce  pathological  effects  in  the  retina  of  the 


EFFECTS    OF    RADIANT    ENERGY   ON    THE    EYE.  687 

aphakic  eye  in  6  days,  while  a  total  daily  exposure  of  g  the  liminal, 
in  this  case  4  minutes,  would  produce  no  effects  even  if  indefinitely 
continued.  These  estimates  do  not  allow  for  the  pupillary  contrac- 
tion, which  would  result  from  the  fixation  of  such  a  bright  source  and 
which  would  in  most  cases  increase  the  necessary  exposures  three  or 
four  times,  or  for  imperfect  fixation.  They  also  do  not  allow  for  the 
thick  cataract  glasses  which  in  most  cases  would  be  worn  and  which 
would  increase  the  necessary  exposures  many  times,  since  a  10  dioptre 
lens  would  be  almost  impenetrable  to  abiotic  radiations.  For  the 
quartz  mercury  vapor  lamp  still  longer  exposures  would  be  required 
owing  to  the  size  and  shape  of  the  light  source  giving  less  concentration 
in  the  image.  It  is,  therefore,  now  apparent  why  there  is  no  known 
case  of  a  human  eye  from  which  the  lens  has  been  removed  in  wrhich 
the  retina  has  been  injured  by  exposure  to  artificial  light,  and  why 
such  injury  is  in  the  highest  degree  improbable. 

In  endeavoring  to  demonstrate  by  direct  experiment  the  possibility 
of  injuring  the  retina  of  the  aphakic  eye  by  abiotic  radiation  we  have 
found  it  difficult  to  obtain  a  satisfactory  eye  for  the  purpose.  While 
it  was  easily  possible  to  remove  the  lens  from  the  rabbit's  eye,  the 
pupil  became  more  or  less  completely  obstructed  in  almost  all  cases. 
In  one  animal,  however,  we  finally  obtained  by  means  of  repeated 
disci  ssions,  a  clear  pupillary  opening  sufficient  to  admit  the  cone  of 
light  from  the  quartz  double  lens  system.  According  to  our  calcu- 
lations an  exposure  of  35  minutes  with  the  light  focussed  upon  the 
pupillary  area  should  have  been  sufficient  to  produce  abiotic  effects 
in  the  retina.  No  allowance,  however,  was  made  for  absorption 
by  the  vitreous  humor.  As  a  matter  of  fact  no  abiotic  effects  could 
be  demonstrated  in  the  retina  although  marked  heat  effects  were 
obtained  in  the  pigment  epithelium  (Exp.  89).  This  experiment 
thus  goes  to  show  that  the  danger  to  the  retina  from  exposing  the 
aphakic  eye  to  abiotic  radiations  is  even  less  than  is  indicated  by  the 
above  calculations. 


BlRCH-HlRSCHFELD's   OBSERVATIONS. 

Since  the  results  of  our  experiments  especially  in  regard  to  the 
retina  are  so  greatly  at  variance  with  those  of  Birch-Hirschfeld  37 
it  may  be  well  to  review  his  experiments  in  some  detail.  This  is  all 
the  more  necessary  because  his  results  and  conclusions  have  not 
hitherto  either  been  confirmed  or  refuted.  His  experiments  consist 
of  two  series.  In  the  first  series  he  separated  out  the  ultra  violet 


688  VERHOEFF  AND   BELL. 

rays  from  a  15  ampere  carbon  arc  lamp  by  means  of  a  quartz  lens 
and  quartz  prism,  and  concentrated  them  upon  the  anterior  focal 
point  of  the  rabbit's  eye  by  means  of  a  second  quartz  lens.  The  diam- 
eter and  focal  length  of  the  latter  he  did  not  mention.  He  exposed 
both  normal  eyes  and  eyes  from  which  he  had  extracted  the  lenses. 
The  latter  were  seven  in  number.  The  length  of  the  exposures  w^ere 
from  one-fourth  hour  to  6  hours.  Following  the  exposure  there  was 
only  slight  hyperemia  of  the  conjunctiva  which  disappeared  in  24 
hours.  The  cornea  and  lens  were  unaffected  even  after  the  6  hours* 
exposure.  The  retina  on  microscopic  examination  showed  the  follow- 
ing changes:  chromatolysis  and  formation  of  vacuoles  in  the  cyto- 
plasm of  the  ganglion  cells.  Loss  of  chromatin  in  both  nuclear  layers, 
the  nuclei  of  the  outer  layer  becoming  homogeneous  and  their  cross 
striations  almost  completely  obscured.  These  changes  were  found 
just  the  same  immediately  after  exposure  as  in  the  course  of  the 
next  12  to  24  hours.  After  a  few  days  they  disappeared  and  the 
ganglion  cells  showed  an  increased  amount  of  chromatin.  In  the 
animal  which  was  exposed  for  6  hours,  however,  vacuoles  were  found 
in  the  ganglion  cells  at  the  end  of  6  days.  In  the  case  of  normal 
rabbits'  eyes  exposed  to  the  same  conditions,  retinal  changes  were 
found  only  when  the  eye  was  removed  immediately  after  exposure 
and  were  said  to  be  simply  those  of  light  adaptation. 

In  the  second  series  of  experiments  he  exposed  the  rabbits'  eyes  to 
a  3  to  4.5  ampere  Finsen  light.  No  statement  is  made  as  to  whether 
or  not  a  quartz  lens  or  water  cell  were  used,  so  it  is  to  be  presumed  they 
were  not.  Also  no  statement  is  made  as  to  the  distance  between  the 
eye  and  the  light.  Ten  eyes  altogether  were  exposed,  two  being 
aphakic.  The  time  of  exposure  was  from  five  to  ten  minutes. 

In  all  cases  there  was  marked  conjunctivitis,  keratitis,  and  iritis  (?), 
but  no  changes  were  ever  found  in  the  lens  capsular  epithelium.  In 
the  retina  the  following  changes  were  found  in  both  the  normal  eye 
and  the  aphakic  eye,  but  wrere  more  pronounced  in  the  latter:  chro- 
matolysis and  formation  of  vacuoles  in  the  cytoplasm  of  the  ganglion 
cells  with  changes  in  the  nuclei  of  the  latter.  Swelling  and  begin- 
ning collapse  of  the  nuclei  of  the  inner  nuclear  layer.  Loss  of  chro- 
matism  in  the  outer  layer.  The  vacuolization  of  the  ganglion  cells 
in  some  cases  persisted  several  weeks.*  When  a  thick  glass  plate 

*  In  a  footnote  Birch-Hirschfeld  stated  that  in  one  aphakic  eye  after  an 
especially  severe  exposure  to  the  iron  arc  he  obtained  well  marked  myelin 
degeneration  of  the  optic  nerve.  He  also  stated  that  he  would  later  give  the 
details  of  this  experiment,  but  we  are  unable  to  find  that  he  has  done  so  up 
to  the  present  time. 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          689 

was  placed  before  the  eye  these  changes  did  not  occur.  The  exact 
length  of  time  after  exposure  when  the  eyes  were  examined  is  not 
stated.  It  also  is  not  stated  whether  or  not  the  changes  could  be 
found  if  the  eyes  were  removed  immediately  after  the  exposures. 

It  is  impossible  for  us  to  accept  the  findings  in  these  experiments 
for  the  following  reasons.  In  the  first  place  the  retinal  changes 
described  were  widespread.  To  obtain  a  widespread  illumination 
of  the  retina,  however,  necessitates  the  use  of  a  quartz  lens  of  extreme 
aperture.  Birch-Hirschfeld  does  not  state  that  he  used  such  a  lens. 
The  widespread  illumination  of  the  retina  also  necessitates  a  greater 
intensity  of  illumination  of  the  cornea  and  lens  than  of  the  retina. 
This  together  with  the  fact  that  the  lens  capsule  receives  in  addition 
rays  of  much  shorter  wave  length  than  can  reach  the  retina  makes  it 
inconceivable  that  the  retina  could  be  injured  under  these  conditions 
without  the  lens  capsule  also  being  affected.  Yet  Birch-Hirschfeld 
states  that  in  neither  series  of  experiments  was  the  intensity  and  dura- 
tion of  exposure  sufficient  to  injure  the  lens.  In  fact  the  abiotic 
intensity  was  so  slight  that  the  corneal  epithelium  was  destroyed  only 
in  one  experiment  in  which  the  cornea  apparently  became  infected. 

On  the  other  hand  if  we  assume  that  Birch-Hirschfeld  used  no  lens 
or  a  lens  of  ordinary  aperture,  the  retinal  lesions,  if  any,  would  have 
been  circumscribed  and  would  not  often  have  been  found  by  his 
method  of  examining  the  eyes.  As  we  shall  show,  with  sufficient  light 
intensity  small  retinal  lesions  can  be  produced  under  these  condi- 
tions, but  they  are  due  to  heat  and  are  entirely  different  from  those 
described  by  Birch-Hirschfeld.  The  radiant  energy  used  by  Birch- 
Hirschfeld,  however,  was  undoubtedly  insufficient  to  produce  such 
an  effect. 

In  his  first  series  of  experiments  it  is  stated  that  the  changes  occurred 
immediately  after  the  exposures.  This  is  inconsistent  with  an  abi- 
otic action  of  light,  since  with  this  there  is  always  a  latent  period. 
Thus  we  found  that  the  epithelial  cells  of  the  lens  capsule  showed 
absolutely  no  change  if  examined  immediately  after  severe  exposure 
to  abiotic  rays. 

Birch-Hirschfeld  holds  that  the  ganglion  cell  changes  he  describes 
represent  a  further  stage  of  light  adaptation.  Yet  he  maintains  that 
they  are  due  to  the  direct  action  of  the  light  on  the  ganglion  cells 
themselves.  He  states  that  there  is  no  reason  to  believe  that  certain 
cells  are  more  susceptible  to  ultra  violet  light  than  others,  yet  he  found 
changes  in  the  retinal  ganglion  cells  and  none  in  the  capsular  epithe- 
lium in  spite  of  the  fact,  just  pointed  out,  that  the  latter  must  have 


690  VERHOEFF  AND   BELL. 

received  light  not  only  of  greater  intensity  but  also  of  shorter  wave 
length  than  did  the  retina. 

We  cannot  then  accept  Birch-Hirschfeld's  findings  because  we  were 
unable  to  obtain  retinal  changes,  although  we  used  light  intensities 
and  exposures  sufficient  to  injure  the  epithelium  of  the  lens  capsule, 
the  stroma  cells  and  endothelium  of  the  cornea  (which  he  did  not). 
Judging  by  the  relatively  slight  histological  changes  found  in  the  cor- 
nea by  Birch-Hirschfeld,  the  intensity  on  the  cornea  of  the  light  used 
by  us  must  have  been  over  fifty  times  as  great  as  that  used  by  him, 
while  some  of  our  exposures  were  nine  times  as  long  as  his  maximum 
exposure  (10  minutes)  to  the  iron  arc.  In  the  case  of  the  aphakic  eye, 
we  obtained  no  ganglion  cell  changes  in  48  hours  although  the  light  in- 
tensity was  so  great  that  the  pigment  epithelium  showed  heat  changes 
in  spite  of  an  interposed  water  cell.  In  Birch-Hirschfeld's  experiments 
the  pigment  epithelium  was  uninjured  although  a  water  cell  was  not 
used.  Finally,  we  cannot  accept  Birch-Hirschfeld's  findings  because 
our  experiments  on  monkeys  and  on  a  human  patient  prove  conclu- 
sively that  the  function  of  the  ganglion  cells  is  not  injured  by  light 
of  the  same  wave  lengths  and  vastly  greater  intensity  than  that  reach- 
ing the  retina  in  Birch-Hirschfeld's  experiments. 

In  connection  with  Birch-Hirschfeld's  findings  the  following  observa- 
tions relating  to  the  ganglion  cells  of  normal  rabbit's  eyes  may  be 
of  significance.  In  the  first  place,  within  the  same  retina  there  is 
great  variation  in  the  amount  of  chromatin  substance  in  the  individual 
ganglion  cells;  two  cells  side  by  side  may  show  a  great  difference  in 
this  respect.*  The  sharpness  with  which  the  Nissl  bodies  stain  in 
thionin  varies  considerably  with  slight  variations  in  the  staining  pro- 
cedure, particularly  as  regards  the  length  of  time  the  sections  have 
been  immersed  in  the  thionin  solution  and  the  degree  of  differentia- 
tion in  alcohol.  The  same  statement  applies  also  to  the  intensity 
with  which  the  nuclear  layers  stain.  While  the  ganglion  cells  of  a 
normal  retina  probably  never  contain  actual  vacuoles,  the  arrange- 
ment of  the  chromatin  particles  is  not  infrequently  such  that  they 
enclose  spaces  which  bear  considerable  resemblance  to  vacuoles. 
Occasionally  a  ganglion  cell  may  contain  an  apparently  degenerated 
nucleus,  and  occasionally  also  a  more  or  less  disintegrated  ganglion 
cell  is  seen.  Possibly  the  injury  to  the  latter  is  produced  by  the 
microtome  knife. 

*  Nissl  bodies  cannot  be  seen  in  fresh  ganglion  cells  so  that  it  is  possible 
that  they  are  formed  after  death.  The  term  chromatolysis  may  therefore  be 
misleading  inasmuch  as  it  means  solution  of  substances  during  life  which  may 
have  never  actually  existed. 


EFFECTS   OF   RADIANT    ENERGY   ON   THE    EYE.  691 

These  observations  are  in  accord  with  those  of  Bach  made  twenty 
years  ago.  Investigating  the  possible  effect  of  fatigue  upon  the 
ganglion  cells  of  the  retina,  Bach  u  made  a  careful  comparison  of 
retinae  of  rabbits  exposed  and  unexposed  to  light.  In  some  cases 
eyes  were  exposed  to  a  Welsbach  light  for  20  hours.  Alcohol  or 
sublimate  fixation  was  used  and  the  sections  stained  by  the  original 
Xissl  method  or  in  thionin.  Contrary  to  the  previous  observation 
of  Mann  235  and  the  later  observations  of  Birch-Hirschfeld,39  he  was 
unable  to  find  that  the  ganglion  cells  of  the  exposed  eye  differed  in 
any  way  from  those  of  the  unexposed.  He  says:  "Ich  geh  zu,  dass 
ich  langere  zeit  im  Zweifel  war  und  bald  diese  bald  jene  Veranderungen 
gefunden  zu  haben  glaubte,  jedoch  alles  anscheinend  Gefundene  Hess 
mich  die  controle  wieder  als  Irrthum  erkennen.  Es  ist  eben  zu 
bedenken,  dass  trotz  gleicher  Schnittdicke,  trotz  des  genau  gleichen 
Verfahrens  beim  Farben  etc.  immerhim  sich  tinctorielle  Unterschiede 

ergeben   konnen Ich   muss  bemerken,  dass  auch  in  normalen 

Netzhauten  an  den  Ganglienzellen  sich  Unterschiede  besonders  hin- 
sichtlich  der  Menge  und  Anordnung,  der  Form  der  farbaren  Plasma- 
schollen  ergeben,  das  auch  normalen  Weise  Vacuolen  in  dem  Zellleib 
gefunden  werden,  das  die  Kerne  sich  verschieden  verhalten  konnen  — 
kurz  ich  konnte  an  den  beleuchteten  Netzhauten  Nichts  warhnehmen 
oder  vermissen  was  ich  nicht  an  normalen,  an  verdunkelten  Netz- 
hauten auch  wahrgenommen  oder  vermisst  hatte." 

Birch-Hirschfeld  37  states  that  also  by  means  of  the  vital  methylene 
blue  staining  method  he  found  chromatolysis,  vacuolization,  and  other 
changes  in  the  retinal  ganglion  cells  of  eyes  that  had  been  exposed 
to  ultra  violet  light,  and  that  such  changes  wrere  absent  in  normal  eyes. 
I  find,  however,  by  this  method  in  the  normal  rabbit's  retina,  appear- 
ances that  correspond  exactly  to  those  described  and  depicted  by 
Birch-Hirschfeld,  including  particularly  the  "vacuoles"  in  the  gan- 
glion cells  which  are  abundantly  present.  The  "vacuoles"  at  first 
glance  appear  to  be  really  such,  but  a  careful  study  of  them  strongly 
suggests  that  they  are  here  due  to  the  cell  reticulum  staining  more 
promptly  and  deeply  than  the  cytoplasm  proper,  and  thus  producing 
an  appearance  of  rounded  spaces.  I  have  also  examined  the  retina  by 
the  vital  methylene  blue  method  48  hours  after  the  exposure  of  one 
hour  to  the  magnetite  arc  and  lens  system  (Exp.  78).  The  results 
obtained  were  identical  with  those  obtained  in  the  case  of  an  un- 
exposed normal  retina. 

In  addition  to  the  experimental  investigation  just  discussed,  Birch- 
Hirschfeld35  has  reported  clinical  observations  in  five  cases  of  pho- 


692  VERHOEFF  AND   BELL. 

tophthalmia  following  exposure  to  the  mercury  vapor  lamp  that  he 
claims  demonstrate  the  pathological  action  of  ultra  violet  light  upon 
the  retina.  In  these  cases  he  found,  for  colors  only,  para-  or  peri- 
central  scotoma,  central  relative  scotoma,  and  constriction  of  the  peri- 
pheral field.  Later24  he  reports  that  after  an  exposure  of  less  than 
|  hour  to  the  Schott  uviol  lamp  he  himself  was  affected  with  mild 
photophthalmia  followed  by  color  field  changes.  He  found  a  relative 
color  scotoma  in  each  eye  beginning  15°  from  the  fixation  point  that 
persisted  6  days.  After  this  had  completely  disappeared  he  exposed 
his  left  eye  to  the  same  light  through  a  colorless  glass  obstructing 
all  waves  less  than  330  MM  in  length  and  obtained  no  changes  of  any 
kind.  He  regarded  this  as  proof  of  his  contention  that  the  field 
changes  previously  obtained  were  due  chiefly  to  waves  between  300  MM 
and  330  MM-  As  a  matter  of  fact,  however,  Hallauer123  has  shown 
that  the  adult  human  lens  absorbs  all  waves  less  than  376  MM  and  most 
of  those  less  than  400  MM  so  that  this  experiment  of  Birch-Hirschfeld 
proves,  if  it  proves  anything,  that  the  field  changes  obtained  in  his 
clinical  cases  and  in  his  own  case  were  chiefly  subjective  or  at  least  did 
not  represent  pathological  conditions.  Moreover,  as  pointed  out 
elsewhere  (page  721)  Birch-Hirschfeld41  himself  has  recently  taken 
exception  to  the  similar  field  changes  reported  by  Jess  20°  in  cases 
of  eclipse  blindness  on  the  ground  that  they  might  well  have  been 
obtained  in  normal  eyes. 


THERMIC  EFFECTS  OF  RADIANT  ENERGY   ON  THE  EYE. 

The  Cornea.  In  passing  through  the  cornea,  light  of  any  wave  length 
is  absorbed  to  some  extent.  Waves  less  than  295  MM  are  completely 
absorbed  while  those  over  315  MM  m  length  (judging  by  the  results 
of  our  experiments)  are  very  slightly  absorbed.  The  absorption  of  the 
latter  is  no  doubt  due  in  part  at  least  to  the  lamellae  of  the  cornea  and 
the  corneal  corpuscles,  which  cause  internal  reflections  and  refrac- 
tions, especially  of  the  relatively  short  waves.  With  ordinary  light 
intensities  the  amount  of  energy  absorbed  is  so  slight  that  no  heat 
effects  are  produced,  but  with  extreme  intensities  it  is  obvious  that 
the  latter  could  be  produced  even  in  the  case  of  visible  rays.  In  five 
of  our  experiments  definite  heat  effects  were  observed  in  the  cornea. 
That  the  effects  were  due  solely  to  accumulated  heat  and  not  in  any 
degree  to  abiotic  action,  is  proved  by  the  character  of  the  changes 


EFFECTS   OF  RADIANT   ENERGY  ON  THE   EYE.  693 

produced,  and  by  the  fact  that  the  epithelial  cells  of  the  cornea  and 
lens  were  unaffected.  The  screens  were  such  that  the  lens  received 
waves  of  the  same  wave  lengths  as  did  the  cornea.  The  corneal 
epithelium  was  unaffected  probably  owing  to  its  being  cooled  by  con- 
tact with  the  air.  In  no  instance  did  the  heat  reach  sufficient  inten- 
sity as  to  cause  pain. 

The  most  marked  heat  effect  on  the  cornea  was  obtained  in  Exp. 
88  in  which  the  rays  from  the  magnetite  arc  after  passing  through  a 
flint  screen  and  water  cell  were  concentrated  for  one  hour  sharply 
upon  the  cornea  by  means  of  the  quartz  double  lens  system.  Toward 
the  end  of  the  experiment  it  was  discovered  that  the  water  cell  had 
leaked,  so  that  for  an  unknown  length  of  time  the  eye  had  been  exposed 
to  infra  red  rays  in  addition  to  the  shorter  waves.  This  undoubtedly 
accounts  for  the  fact  that  in  no  other  experiment  was  such  a  marked 
heat  effect  produced,  and  that  no  effect  was  produced  in  Exp.  85 
in  which  the  same  conditions  obtained  except  that  the  water  cell  did 
not  leak  and  the  exposure  was  longer.  24  hours  after  the  exposure 
the  affected  area  was  hazy  and  swollen  but  the  eye  was  free  from 
inflammatory  reaction.  On  microscopic  examination  48  hours  after 
the  exposure  the  epithelium  was  everywhere  normal.  The  stroma 
was  swollen  to  over  twice  its  normal  thickness  and  stained  faintly 
in  eosin.  Within  the  central  portion  of  the  exposed  area  not  a 
single  corneal  corpuscle  could  be  seen.  At  the  periphery  the  transi- 
tion into  normal  cornea  was  abrupt  as  regards  the  corpuscles  but 
relatively  gradual  as  regards  the  stroma.  In  the  transition  region 
the  corpuscle  towards  the  normal  side  were  in  active  proliferation, 
many  of  them  showing  mitosis,  while  from  here  inward  they  suddenly 
became  invisible.  The  endothelium  in  the  exposed  region  was  for 
the  most  part  completely  absent,  but  in  some  places  a  few  faintly 
stained  cells  still  adhered  to  Descemet's  membrane.  The  cornea  was 
everywhere  practically  free  from  leucocytic  infiltration.  The  iris 
showed  a  few  minute  hemorrhages  around  the  pupil  undoubtedly  due 
to  heat,  since,  as  stated,  the  lens  capsule  was  unaffected.  (PI.  1, 
Fig.  3.) 

In  the  second  experiment  (Exp.  92)  sunlight  was  focussed  45 
minutes  upon  the  cornea  by  means  of  a  large  quartz  lens  after  passing 
through  a  blue  uviol  screen  and  a  .001%  aqueous  solution  of  auramine 
O.  Here  the  heat  effect  was  similar  but  less  marked  than  that  just 
described.  The  effect  on  the  corneal  corpuscles  was  about  as  great, 
and  the  appearance  of  the  stroma  about  the  same  except  that  it  was 
much  less  swollen.  The  corneal  epithelium,  the  iris,  and  the  lens 
epithelium,  M^re  unaffected. 


694  VERHOEFF  AND   BELL. 

The  third  experiment  (Exp.  81)  was  similar  to  the  first  except  that 
the  flint  screen  allowed  waves  down  to  305  /JL/JL  to  pass  and  that  the 
water  cell  did  not  leak.  The  exposed  corneal  area  was  clear  immedi- 
ately after  the  exposure,  but  20  minutes  later  was  found  to  be 
distinctly  hazy.  The  epithelium  at  no  time  stained  with  fluorescine. 
On  microscopic  examination  of  the  eye,  enucleated  three  days  after 
the  exposure,  the  corneal  stroma  was  found  to  be  swollen  in  a  rather 
sharply  defined  area.  The  epithelium  was  normal.  The  corneal 
corpuscles  in  the  middle  third  of  the  cornea  showed  active  prolifera- 
tion, but  in  the  posterior  third  had  for  the  most  part  disappeared. 
The  endothelium  was  absent  behind  the  exposed  area.  The  iris  and 
lens  epithelium  were  normal. 

In  the  fourth  experiment  (Exp.  84)  a  flint  screen  transparent  to 
waves  down  to  310  /j,fj,  was  used  and  the  exposure  was  one  and  one  half 
hours.  The  exposed  corneal  area  was  found  to  be  hazy  within  one 
hour  after  the  exposure.  On  microscopic  examination  of  the  eye, 
enucleated  four  days  after  the  exposure,  the  corneal  stroma  was  found 
very  slightly  swollen  and  to  stain  less  strongly  in  eosin  in  its  posterior 
layers.  The  corneal  corpuscles  showed  marked  proliferation  in  the 
posterior  portion  of  the  stroma  and  the  endothelium  was  absent 
behind  the  exposed  area.  The  iris  and  lens  epithelium  were  normal. 

In  the  fifth  experiment  (Exp.  90)  a  flint  screen  (315  /*/*)  was  used 
and  the  conditions  were  the  same  as  in  the  first  experiment  with 
the  important  differences  that  the  water  cell  was  omitted  and  the 
exposure  was  only  30  minutes.  Distinct  haziness  of  the  cornea 
was  observed  within  20  minutes  and  within  24  hours  became  very 
marked.  On  microscopic  examination  (48  hours)  the  cornea  showed 
changes  similar  to  and  almost  as  marked  as  those  of  Experiment 
88.  The  corneal  epithelium  and  lens  epithelium  were  unaffected. 


COMBINED  THERMIC  AND  ABIOTIC  EFFECTS  OF  RADIANT  ENERGY 
ON  THE  CORNEA. 

In  four  other  experiments  in  which  the  exposures  were  prolonged, 
both  abiotic  and  heat  effects  were  obtained  in  the  cornea.  The 
screens  used  were  transparent  to  waves  less  than  305  /*/*  to  298  MJ. 
in  length  and  the  exposures  were  from  one  to  one  and  a  half  hours. 
In  two  of  the  experiments  (Exps.  78  and  79)  abiotic  effects  were  indi- 
•cated  by  loss  of  corneal  epithelium  and  characteristic  changes  in  the 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          695 

lens  epithelium,  and  heat  effects  by  the  haziness  of  the  cornea  occurring 
within  30  minutes  after  the  exposure  as  well  as  by  the  slightness 
of  the  conjunctival  reaction.  Combined  effects  were  also  shown  by 
the  microscopic  examinations,  the  corneal  corpuscles  being  completely 
invisible  in  the  posterior  layers  of  the  cornea,  but  present  and  showing 
characteristic  abiotic  effects  in  the  anterior  layers. 

The  other  two  experiments  were  of  especial  interest  because  they 
showed  the  limit  in  respect  to  wave  length  beyond  which  we  were 
unable  to  obtain  abiotic  effects.  The  same  screen  305  /JL/JL  was  used 
as  in  Exp.  81  just  referred  to,  in  which  only  heat  effects  were  obtained, 
but  the  exposures  were  longer.  In  Exp.  82  the  exposure  was  If  hours 
and  haziness  of  the  cornea  was  noted  within  30  minutes  afterwards. 
The  lens  epithelium  was  unaffected,  and  the  only  evidence  of  abiotic 
action  was  a  slight  loss  of  corneal  epithelium  occurring  after  24  hours. 
The  heat  effects  on  the  other  hand,  were  very  marked.  The  corneal 
endothelium  was  destroyed  in  the  exposed  region  and  only  an  occa- 
sional corpuscle  could  be  seen  even  in  the  anterior  layers  of  the  stroma, 
so  that  any  possible  abiotic  effects  on  the  corneal  corpuscles  were 
masked  by  the  heat  effects.  At  the  periphery  of  the  exposed  area  the 
corpuscles  were  in  active  proliferation  at  the  end  of  48  hours.  In  Exp. 
83  the  conditions  were  the  same  except  that  the  light  was  focussed 
upon  the  surface  of  the  lens  instead  of  upon  the  cornea,  and  that  the 
exposure  was  interrupted  for  an  hour  at  the  end  of  the  first  30  minutes. 
Haziness  of  the  cornea  was  noted  within  50  minutes  after  the  first 
exposure.  Following  the  second  exposure  there  was  no  loss  of  corneal 
epithelium  and  the  only  evidence  of  abiotic  action  was  a  slight  effect 
on  the  lens  epithelium.  The  cells  were  slightly  swollen  in  a  small 
area  and  a  few  of  them  contained  characteristic  granules.  The  heat 
effect  on  the  cornea  was  about  the  same  as  in  the  preceding  experi- 
ment. 

According  to  the  foregoing  experiments  with  the  double  lens  system, 
after  an  exposure  of  if  hours  through  a  water  cell  and  flint  screen 
(315/i/z)  no  changes  are  produced;  after  an  hour's  exposure  through  a 
screen  (310  /JL/JL),  slight  heat  changes;  through  screen  (305  /JL/JL)  marked 
heat  changes;  and  through  still  more  transparent  screens,  marked 
heated  changes  combined  with  abiotic  effects.  With  the  flint  screen 
(315  fjifj,)  but  without  a  water  cell,  marked  heat  changes  are  produced 
after  30  minutes  exposure,  the  heat  effect  of  the  short  waves  here 
being  reenforced  by  infra  red  waves.  It  is  evident  from  these  results 
that  the  specific  absorption  of  the  cornea  with  respect  to  wave  length 
does  not  end  abruptly,  but  gradually  diminishes  from  295  MJL  to  some- 


696  VERHOEFF  AND   BELL. 

what  beyond  315  IJL/J,.  It  is  also  evident  that  the  energy  absorbed 
from  waves  of  305  /zju  or  over  in  length,  is  converted  almost  exclusively 
into  heat,  only  the  slightest  traces  of  abiotic  action  being  obtained 
with  waves  of  305  nn  in  length  after  the  most  intense  and  prolonged 
exposures. 

It  will  be  seen  that  the  abiotic  effects  and  heat  effects  of  radiant 
energy  upon  the  tissues  are  essentially  different.  In  the  case  of  heat, 
a  certain  critical  temperature  is  required  before  any  effect  is  produced. 
This  is  shown  by  the  sharp  transition  from  normal  into  injured  corneal 
corpuscles  at  the  periphery  of  the  exposed  area,  and  also  by  the  fact 
that  the  epithelium,  being  kept  cool  by  contact  with  the  air,  remains 
unaffected.  The  heat  effect  therefore  does  not  vary  in  direct  ratio 
with  the  intensity  of  exposure,  obviously  due  to  the  fact  that  dissipa- 
tion of  heat  enters  into  the  equation.  In  the  case  of  abiotic  action 
on  the  other  hand  the  effect  varies  directly  with  the  intensity  of  the 
exposure.  Heat  of  an  intensity  just  below  that  sufficient  to  cause 
cell  destruction,  causes  cell  proliferation.  Abiotic  action  does  not 
directly  cause  cell  proliferation  no  matter  how  intense  or  how  slight 
the  exposure.  Lastly,  heat  does  not  produce  the  eosinophilic  and 
basophilic  granules  in  the  cytoplasm  that  are  produced  by  exposure 
to  abiotic  radiation. 

On  the  other  hand,  while  it  is  evident  that  heat  does  not  produce 
effects  similar  to  those  produced  by  moderate  exposures  to  abiotic 
waves,  extreme  exposures  to  the  latter  may  produce  effects  not  unlike 
the  severe  effects  of  heat.  Thus  we  have  shown  that  severe  exposures 
to  waves  shorter  than  295  n/j.  in  length  may  lead  to  complete  disap- 
pearance of  the  corneal  corpuscles  and  marked  swelling  of  the  corneal 
stroma.  In  the  case  of  heat,  however,  the  posterior  layers  of  the 
cornea  are  more  affected  than  the  anterior  layers  while  in  the  case  of 
abiotic  action  the  reverse  is  true. 


THERMIC  EFFECTS  OF  RADIANT  ENERGY  UPON  THE 
IRIS  AND  LENS. 

In  Experiment  97  in  which  the  eye  was  exposed  for  one  minute 
through  a  uviol  screen  to  sunlight  concentrated  by  the  large  mirror, 
the  pigmented  iris  was  severely  burned  in  the  exposed  area,  showing 
complete  hyaline  necrosis.  The  lens  epithelium  examined,  after  48 
hours,  was  unaffected  in  the  pupillary  area,  but  beneath  the  pupillary 


EFFECTS   OF   RADIANT   ENERGY   ON  THE   EYE.  697 

margin  it  showed  an  incomplete  ring  which  under  the  low  power  of 
the  microscope  resembled  the"  wall  produced  in  other  experiments  by 
abiotic  radiations.  Examination  under  a  higher  power  however, 
showed  that  the  appearance  was  due  chiefly  to  the  fact  that  the  cells 
were  here  in  a  state  of  active  proliferation,  almost  every  cell  being  in 
some  stage  of  mitosis.  It  was  evident  that  the  heat  from  the  pigment 
layer  of  the  iris,  where  the  latter  was  in  contact  with  the  lens  capsule, 
had  stimulated  the  cells  of  the  latter  to  proliferation.  It  is  note- 
worthy that  in  Experiment  99  in  which  the  exposure  was  1^  minutes 
but  in  which  the  iris  was  unpigmented,  neither  the  iris  or  lens 
capsule  was  affected. 

In  none  of  our  experiments  was  the  lens  injured  by  the  heat  gener- 
ated by  the  stoppage  of  rays  within  its  own  substance.  That  clouding 
of  the  lens  can  be  so  produced,  however,  even  by  visible  rays  alone, 
with  sufficient  intensity  and  prolonged  exposure,  has  already  been 
demonstrated  by  Czerny  85  and  Deutschman  89  in  the  case  of  sunlight, 
and  by  Herzog  176  who  used  the  carbon  arc  and  suitable  filters. 

The  iris  in  no  other  experiment  showed  heat  effects  comparable  to 
those  just  described.  In  most  of  the  experiments  with  the  magnetite 
arc  and  double  lens  system  the  iris  was  not  greatly  exposed  to  the  light 
owing  to  the  artificial  mydriasis,  but  in  Experiment  88  in  which  the 
most  intense  heat  effect  was  obtained  in  the  cornea,  the  iris  showed 
hemorrhages  near  the  pupil.  In  Experiments  83  and  90  the  iris 
became  greatly  contracted  towards  the  end  of  the  exposures,  and 
remained  so  for  several  hours,  but  again  dilated  within  24  hours. 


THERMIC  EFFECTS  OF  RADIANT  ENERGY  UPON  THE  RETINA. 

In  a  number  of  our  experiments,  some  of  which  were  made  with 
other  purposes  in  view,  we  obtained  heat  effects  in  the  retina  in  spite 
of  an  interposed  water  cell  5  cm.  thick.  They  were  obtained  mainly 
in  two  ways,  one  by  the  use  of  sunlight  reflected  from  a  silvered 
glass  concave  mirror  26  cm.  in  diameter  and  1.5  meters  in  focal  length, 
and  the  other  by  the  use  of  the  magnetite  arc  light  concentrated  by  the 
single  quartz  lens  system.  A  full  description  of  the  mirror  and  the 
calculated  energy  derived  from  it  is  given  on  page  721.  The  calcu- 
lated energy  on  the  retina  given  by  the  quartz  single  lens  system  is 
given  on  page  724.  The  burns  were  obtained  through  screens  that 
obstructed  all  waves  less  than  335  MJ.  in  length  as  well  as  through 


698  VERHOEFF   AND   BELL. 

more  transparent  screens.  In  the  case  of  sunlight  the  exposures 
were  from  one-fourth  second  to  one  and  one-half  minutes,  and  the 
resulting  burns  were  always  severe,  the  retinal  tissue  being  actually 
coagulated  as  will  be  described.  In  the  case  of  the  magnetite  arc  the 
exposures  were  from  ten  minutes  to  one  hour  and  the  burns  were  much 
less  severe.  In  addition  to  these,  heat  effects  involving  the  pigment 
epithelium  alone  were  obtained  in  two  experiments  with  the  quartz 
double  lens  system  (Exps.  88  and  89)  in  each  of  which  a  large  area  of 
the  fundus  was  illuminated.  One  of  these  was  in  the  case  of  an 
aphakic  eye,  and  the  other  in  a  case  of  exposure  without  a  water  filter. 
The  significance  of  these  experiments  in  connection  with  the  questions 
of  eclipse  blindness  and  allied  phenomena  is  discussed  elsewhere 
(page  720). 

That  the  severe  effects  produced  by  concentrated  sunlight  were  due 
to  heat  was  obvious  from  their  histological  appearances  and  from  the 
fact  that  the  light  intensity  at  the  focus  was  found  in  all  cases  to 
be  sufficient  quickly  to  ignite  a  match  or  piece  of  paper.  That  the 
relatively  slight  effects  produced  by  the  magnetite  arc  were  also  due 
to  heat,  was  obvious  from  the  fact  that  only  the  pigment  epithelium 
and  outer  retinal  layers  were  affected  and  sometimes  the  pigment 
layer  alone.  If  the  effects  had  been  due  to  the  abiotic  action  of  light 
the  inner  nuclear  layer  and  ganglion  cells  would  necessarily  have  been 
equally  or  even  more  greatly  affected.  Moreover,  as  we  have  already 
shown,  when  the  corneal  epithelium  and  lens  epithelium  were  exposed 
to  light  of  greater  intensity  and  shorter  wave  lengths  than  was  the 
retina  in  these  experiments,  and  for  a  much  longer  time,  no  changes 
were  produced  in  them.  Thus  in  Experiment  53  a  heat  effect  in 
the  retina  was  obtained  after  12  minutes  exposure  to  light  passing 
through  the  lens  of  the  eye,  that  is,  to  waves  longer  than  330  p-p., 
whereas  in  Experiment  85  no  effect  was  produced  on  the  cornea  after 
an  exposure  of  if  hours  to  light  of  greater  intensity  containing  wave 
lengths  as  short  as  315  /x/z.  This  is  easily  explicable  on  the  assumption 
that  the  retinal  changes  under  consideration  were  due  to  heat,  since 
the  cornea  and  lens  must  each  absorb  a  far  less  proportion  of  visible 
and  infra  red  rays  that  reach  them  than  does  the  pigment  epithelium 
of  the  retina.  On  the  other  hand  it  is  absolutely  inexplicable  on  the 
assumption  that  the  retinal  changes  were  due  to  abiotic  action,  since 
it  is  inconceivable  that  the  corneal  and  lens  epithelium  would  be  un- 
affected by  abiotic  action  of  light  sufficient  to  produce  nuclear  frag- 
mentation in  the  outer  muclear  layer  and  pigment  epithelium.  The 
character  of  the  histological  changes  clearly  indicates  that  the  heat 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          699 

conversion  took  place  chiefly  in  the  pigment  epithelium  and  inner 
layers  of  the  chorioid,  and  that  the  outer  layers  of  the  retina  proper 
were  affected  by  the  heat  conducted  therefrom. 

An  interesting  problem  is  the  exact  determination,  under  various 
conditions,  of  the  minimum  intensity  and  duration  of  exposure  to 
visible  and  infra  red  rays  necessary  to  produce  heat  effects  on  the  ret- 
ina. A  discussion  of  this  problem  will  be  found  on  pages  721  and  732. 

The  experiments  in  which  heat  effects  on  the  retina  were  obtained 
by  means  of  the  magnetite  arc  were  Experiments  53,  55,  57  58,  59, 
88,  89. 

Following  are  the  experiments  with  sunlight  concentrated  by  the 
large  mirror. 


EXPERIMENTS. 
Sunlight  Focussed  on  Cornea  by  Large  Mirror. 

Experiment  95.  Without  water  cell  or  screen.  Pigmented  eye. 
Three  exposures,  5  second,  \  second,  and  10  seconds  respectively. 
No  inflammatory  reaction.  Enucleation  at  end  of  33  days.  Lens 
epithelium  normal.  Three  burned  areas  in  fundus  of  different  grades 
of  severity. 

Experiment  96.  Water  cell.  Flint  glass  screen  (335  MM)-  Albino. 
Exposed  4  seconds.  No  inflammatory  reaction.  Lid  reflex  to  light 
abolished.  Enucleation  at  end  of  48  hours.  Two  contiguous  burned 
areas  in  fundus,  one  exactly  on  disc.  Marked  hemorrhagic  retinitis. 
Slight  hemorrhage  from  retina  into  vitreous. 

Experiment  97.  Blue  uviol  screen.  No  water  cell.  Pigmented 
eye.  Exposed  1  minute.  After  1  hour:  Pupil  contracted  to  \  normal 
size,  does  not  react  to  light.  After  24  hours:  Lid  margins  inflamed, 
lower  one  ulcerated,  no  lid  reflex  to  light.  Cornea  clear.  After  3 
days :  Cornea  shows  purulent  infiltrate  below  (infected  from  ulcerated 
lid).  Enucleation.  Fundus  shows  two  contiguous  burned  areas, 
one  at  margin  of  disc.  Microscopic  examination:  (3  days):  Slight 
purulent  infiltration  of  cornea.  Hyaline  necrosis  of  iris.  Lens  epi- 
thelium normal  in  pupillary  area,  shows  proliferative  changes  beneath 
pupillary  margin  (heat  effect  due  to  contact  with  heated  iris.  See 
page  696). 

Experiment  98  (PI.  4,  Fig.  14).  Water  cell.  No  screen. 
Albino.  Exposed  14  seconds  (misty  day).  No  inflammatory  reac- 


700  VERHOEFF   AND    BELL. 

tion.  Enucleation  at  end  of  6  days.  Fundus  shows  burned  area  just 
beneath  optic  disc.  Lens  epithelium  normal. 

Experiment  99.  Blue  uviol  screen.  Water  cell.  Albino.  Ex- 
posed If  minutes.  No  inflammatory  reaction.  Enucleation  at  end 
of  12  days.  Fundus  shows  burned  area  undergoing  repair.  Cornea, 
lens  epithelium,  and  iris  normal. 

Experiment  100.  Blue  uviol  screen.  Water  cell.  Albino.  Total 
exposure,  10  minutes,  one  second  on,  one  second  off.  No  inflamma- 
tory reaction.  Enucleation  at  end  of  7  days.  Retina  shows  no 
burned  areas.  Cornea,  lens  epithelium,  and  iris,  normal. 

Experiment  101.  Blue  uviol  screen.  No  water  cell.  Pigmented 
eye.  220  exposures,  \  second  each,  with  intervals  of  1  to  3  seconds. 
No  inflammatory  reaction.  Fundus  normal. 


CHARACTER  OF  THE  THERMIC  EFFECTS  PRODUCED  IN  THE  RETINA. 

In  the  experiments  in  which  the  pigment  epithelium  alone  was 
affected  no  changes  were  noted  macroscopically.  In  most  of  the  other 
experiments  the  lesions  could  be  seen  with  the  ophthalmoscope  or 
better  still  on  opening  the  eye  after  enucleation.  They  appeared  as 
sharply  defined  reddened  spots.  Some  of  those  obtained  after  ex- 
posure to  sunlight  showed  blood  extending  from  them  into  the  vitreous 
humor.  Some  of  the  spots  were  observed  only  after  the  eye  was 
placed  in  Zenker's  fluid.  In  Experiment  96  in  which  a  burned  area 
involved  the  optic  disc,  there  was  intense  hemorrhagic  retinitis  ap- 
parently due  to  thrombosis  of  the  central  vein.  The  spots  produced 
by  sunlight  measured  about  2.5  mm.  in  diameter.  Those  produced 
by  the  magnetite  arc  and  single  lens  system  were  about  3  mm.  in 
diameter  as  measured  under  the  microscope  with  reference  to  the 
effects  on  the  pigment  epithelium,  but  only  about  1  mm.  in  diameter 
as  measured  with  reference  to  the  effects  on  the  retina  proper  when 
this  was  involved.  This  concentration  of  the  effects  in  the  center  of 
the  area  was  no  doubt  due  to  two  facts,  one  being  that  the  light  was 
actually  more  intense  here,  and  the  other  that  towrards  the  periphery 
of  the  area  the  heat  generated  in  the  pigment  epithelium  became 
rapidly  dissipated. 

Microscopical:  The  most  striking  feature  of  all  the  burned  areas 
whether  due  to  long  or  short  exposures  was  their  sharp  demarcation, 
illustrating  again  here  as  in  $ie  case  of  the  cornea  how  sharply  critical 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          701 

is  the  temperature  required  to  injure  tissues.  In  all  cases  the  pigment 
epithelium  was  the  most  severely  affected  of  any  portion  of  the  retina, 
and  in  the  slightest  burns  it  alone  was  affected.  This  was  true  also  in 
albinotic  rabbits  in  which  the  epithelium  was  free  from  pigment.  The 
other  structures  were  affected  in  the  following  order  according  to  the 
intensity  of  the  action,  the  rods  and  cones,  the  chorio-capillaris,  the 
outer  nuclear  layer.  The  inner  nuclear  layer,  the  ganglion  cells,  and 
nerve  fibre  layer,  were  affected  only  after  extremely  intense  exposures 
and  in  our  experiments  were  not  affected  after  exposures  to  the  magne- 
tite arc  but  only  when  concentrated  sunlight  was  used. 

The  slightest  change  that  can  be  definitely  made  out  in  the  pig- 
ment epithelium  48  hours  after  exposure  consists  in  the  cytoplasm 
of  a  greater  or  less  number  of  cells  staining  intensely  in  eosin.  When 
the  effect  is  somewhat  greater,  vacuoles  appear  and  may  be  so  large 
and  numerous  that  the  cells  appear  almost  completely  transparent, 
the  cytoplasm  showing  a  delicate  reticulum  with  the  minute  nodes  at 
the  junction  points.  In  case  the  epithelium  is  pigmented  the  pigment 
appears  to  be  separated  from  the  membrane  of  Bruch  by  large  vacuoles, 
and  the  nucleus  may  show  marked  pycknosis.  When  the  effect  is  still 
greater  the  cell  reticulum  completely  disappears  leaving  only  the 
nucleus  in  the  clear  space  thus  formed.  The  nucleus  may  show 
fragmentation  or  simply  chromatolysis.  The  basophilic  and  eosino- 
philic  granules  characteristic  of  abiotic  action  are  not  seen.  In  the 
somewhat  more  severe  burns  the  pigment  cells  entirely  disappear 
leaving  only  the  pigment.  In  one  eye  examined  six  days  after  ex- 
posure the  injured  epithelium  is  found  replaced  by  epithelium  which 
has  evidently  grown  in  from  the  periphery,  but  between  the  new  layer 
and  the  rods  and  cones  numerous  swollen  vaculated  and  otherwise 
altered  pigment  cells  remain.  The  changes  in  the  pigment  epithelium 
are  best  seen  in  plane  section,  and  to  determine  the  character  of  the 
slightest  changes  it  is  important  to  compare  the  appearances  seen  in 
the  exposed  eye  with  those  of  a  normal  eye. 

Forty-eight  hours  after  exposures  sufficient  to  affect  the  rods  and 
cones,  the  outer  limbs  of  the  latter  are  found  to  be  broken  up  into 
coarse  granules,  while  the  inner  limbs  are  swollen  to  large  bladder-like 
structures  each  containing  a  few  fine  granules.  There  may  also  be  a 
greater  or  less  number  of  red  blood  corpuscles  among  the  rods  and 
cones  due  to  diapedesis  from  the  chorio-capillaris,  and  also  a  certain 
amount  of  serum.  When  the  outer  nuclear  layer  is  affected,  the  nuclei 
lose  their  peculiar  cross  striations,  becoming  intensely  pycknotic 
and  some  of  them  undergoing  fragmentation.  With  this  degree  of 


702  VERHOEFF   AND   BELL. 

injury  the  pigment  cells  have  disappeared,  and  fragmented  nuclei 
can  sometimes  be  seen  in  the  inner  layers  of  the  chorioid.  The  inner 
layers  of  the  retina,  including  the  ganglion  cells,  remain  normal  in 
appearance.  (PI.  4,  Fig.  12.) 

In  the  experiments  in  which  sunlight  was  used,  as  already  noted, 
much  more  intense  heat  effects  are  found  in  the  retina  and  chorioid. 
Here  the  inner  layers  of  the  retina  are  disintegrated  while  the  outer 
layers  appear  intact.  This  is  undoubtedly  due  to  the  fact  that  the 
latter  have  been  coagulated  and  thus  fixed  by  the  lieat.  At  the 
periphery  of  the  area  the  appearance  is  reversed,  the  inner  layers 
being  normal  while  the  outer  layers  show  the  less  marked  changes 
already  described. 

Two  to  six  days  after  such  an  exposure  the  coagulated  rods  and  cones 
maintain  their  normal  appearance  except  that  they  stain  abnormally 
deeply  in  eosin.  The  nuclei  of  the  external  nuclear  layer  are  likewise 
coagulated,  but  have  lost  their  cross  striations  and  stain  more  deeply 
than  normal.  The  internal  nuclear  layer  shows  different  appearances 
in  different  places  evidently  according  to  the  heat  intensity.  In 
some  places  the  nuclei  still  take  the  basic  stain  and  show  fragmenta- 
tion. In  others  they  stain  in  eosin  and  are  not  disintegrated,  while  in 
still  others  they  have  entirely  disappeared.  The  nerve  fibre  layer  is 
completely  disintegrated  and  the  ganglion  cells  have  entirely  disap- 
peared or  stain  only  in  eosin.  At  the  periphery,  the  ganglion  cells 
with  their  Nissl  bodies  stain  less  and  less  in  thionin  as  the  burned 
area  is  approached  until  they  become  entirely  eosinophilic.  The 
inner  surface  of  the  retina  is  in  some  cases  coated  with  a  thick  layer 
of  fibrin.  The  pigment  epithelium  is  coagulated  and  retains  its 
normal  position  in  the  exposed  area.  At  the  periphery  it  is  disin- 
tegrated. The  chorioid  behind  it  shows  large  extra vastions  of  blood 
and  marked  nuclear  fragmentation.  There  is  no  cellular  infiltration, 
purulent  or  otherwise,  of  either  the  chorioid  or  retina.  (PL  4,  Fig.  14.) 

After  two  months  the  retina  is  found  replaced  by  neuroglia  con- 
taining migrated  pigment  cells.  In  some  cases  the  chorioid  is  appar- 
ently normal  and  the  pigment  epithelium  reformed.  In  others  the 
latter  is  absent  and  the  chorioid  replaced  by  two  or  three  layers  of 
a  vascular  fibrous  tissue. 


EFFECTS    OF   RADIANT    ENERGY   ON    THE    EYE.  703 


THEORY   OF   ACTION   OF  RADIANT  ENERGY  ON  THE  TISSUES. 

A  useful  conception  of  the  effects  of  radiant  energy  upon  the  tissues 
of  the  body  is  that  the  heat  effect  is  due  to  increased  molecular  motion 
while  the  abiotic  effect  is  due  to  direct  atomic  disintegration  of  the 
molecules  with  immediately  resulting  chemical  changes.  The  first 
effect  of  the  increased  molecular  motion  is  to  produce  a  physical 
change  analogous,  for  example,  to  the  melting  of  ice.  When  the 
motion  reaches  a  certain  critical  rate  the  molecules  are  broken  up  and 
various  chemical  changes  result.  Both  heat  effects  and  abiotic 
effects  theoretically  may  be  produced  by  rays  of  any  wave  length, 
but  practically  in  the  case  of  short  waves  the  heat  effect  is  generally 
negligible,  while  in  the  case  of  long  waves  the  abiotic  effect  is  negli- 
gible. Our  experiments  show  that  for  human  cells  the  abiotic  effect 
becomes  negligible  within  a  very  short  range  of  wave  lengths,  that  is 
between  305  and  310/zju.  For  bacteria  it  becomes  negligible  still 
sooner,  at  less  than  295  ju/z.  Under  ordinary  conditions  heat  effects 
are  also  negligible  here,  and  in  fact  all  through  the  visible  spectrum, 
although  with  extreme  intensities  such  as  afforded  by  concentrated 
sunlight  they  may  be  produced,  as  in  eclipse  blindness,  for  instance. 
It  is  in  reality  due  to  the  fact  that  abiotic  effects  and  heat  effects 
are  negligible  in  the  region  of  the  spectrum  indicated,  that  sunlight 
under  usual  conditions  is  not  destructive  to  human  life.  This  fact, 
considered  from  the  standpoint  of  evolution,  suggests  a  relation  of 
light  to  the  origin  and  structure  of  living  matter,  but  a  discussion  of 
this  aspect  of  the  subject  would  lead  too  far. 

Since  according  to  this  conception  the  abiotic  action  of  light  is 
directly  upon  the  structure  of  the  molecules,  slight  chemical  changes 
are  produced  after  almost  infinitesimal  exposures.  Theoretically,  of 
course,  there  is  a  limit  of  exposure  below  which  no  disintegrating  effect 
is  produced  upon  the  molecules,  so  that  a  series  of  such  short  expo- 
sures would  produce  no  summative  effect.  Practically,  however,  this 
would  be  impossible  to  demonstrate  in  the  case  of  living  cells.  On  the 
other  hand,  in  the  case  of  living  cells  summation  of  the  effects  of  a 
series  of  exposures,  if  the  intervals  were  too  long,  would  not  accurately 
occur,  since  the  repair  of  the  injury  would  take  place  to  a  greater  or 
less  extent.  Thus  we  have  found  in  the  case  of  the  corneal  cells  that 
summation  of  effects  becomes  much  less  exact  when  the  intervals 
of  exposure  are  over  twenty-four  hours. 


704  VERHOEFF  AND   BELL. 

In  the  case  of  heat,  deleterious  effects  on  the  tissues  must  likewise 
be  due  to  chemical  changes.  Since,  however,  these  changes  take 
place  only  when  the  molecules  have  reached  a  certain  rate  of  motion, 
under  ordinary  conditions  a  measurable  time  interval  must  elapse 
before  they  begin.  The  length  of  the  time  interval  depends  upon  the 
intensity  of  the  light  and  upon  the  rapidity  with  which  dissipation 
of  heat  occurs,  and  thus  varies  greatly  under  different  conditions. 
Under  ordinary  conditions,  however,  the  time  interval  is  of  consider- 
able length,  so  that  a  series  of  exposures  does  not  produce  a  total 
effect  equal  to  that  of  a  continuous  exposure  of  the  same  total  length, 
and  may  not  produce  any  effect  at  all.  From  a  practical  standpoint 
therefore  this  fact  constitutes  a  fundamental  difference  between  the 
abiotic  effects  and  the  heat  effects  of  radiant  energy. 

Unless  light  rays  are  absorbed  by  substances  they  can  of  course 
produce  no  effect  upon  them.  Thus,  as  we  have  shown,  waves  over 
295  fjifj,  in  length  unless  extremely  intense  have  no  effect  on  the  corneal 
stroma  which  is  relatively  transparent  to  them  but  have  a  markedly 
deleterious  effect  on  the  corneal  corpuscles  which  absorb  them.  It 
does  not  necessarily  follow,  however,  that  because  light  rays  fail  to 
pass  through  a  given  substance  they  must  produce  an  effect  upon  it. 
For  they  may  simply  be  changed  into  light  waves  of  longer  wave  length 
(fluorescence)  or  their  energy  dissipated  in  the  form  of  heat  of  an  in- 
tensity too  low  to  produce  any  changes.  Both  of  these  transforma- 
tions must  take  place  in  the  case  of  the  lens  of  the  eye  since  light 
waves  are  constantly  being  stopped  in  it.  That  fluorescence  actually 
occurs  in  the  lens  is,  of  course,  well  known  and  easily  demonstrated. 

Assuming  that  the  abiotic  action  of  light  of  given  wave  lengths 
upon  protoplasm  is  directly  proportional  to  the  coefficient  of  absorp- 
tion of  the  protoplasm  for,  that  wave  length,  Henri 1()3  and  his  wife 
have  determined  this  coefficient  for  egg  albumin  and  a  large  number 
of  waves.  The  curve  plotted  from  their  results  given  elsewhere 
(page  645)  shows  that  the  absorption  becomes  practically  nil  at  and 
near  310  /*/*,  so  that  the  abiotic  action  must  be  very  slight  here. 
Moreover,  since  this  method  does  not  allow  for  the  fact  that  the 
absorbed  rays  produce  heat  as  well  as  abiotic  effects,  the  abiotic 
action  is  undoubtedly  less  than  is  indicated  by  the  curve  of  absorp- 
tion. These  results,  therefore,  confirm  in  a  striking  manner  those 
obtained  by  us  by  actual  experiments  on  the  cornea. 

The  preceding  discussion  has  concerned  mainly  the  direct  effects 
of  light  upon  the  molecules  of  the  tissues  without  reference  to  histo- 
logical  and  clinical  manifestations.  The  latter  are  of  course,  too 


EFFECTS   OF   RADIANT    ENERGY   ON   THE   EYE. 


705 


complicated  for  complete  analysis  since  fully  to  understand  them 
would  require  a  knowledge  not  only  of  the  chemical  changes  originally 
produced,  but  of  the  vital  processes  of  the  cells.  An  interesting 
question  in  regard  to  them  is  that  concerning  latency  of  their  appear- 
ance. In  the  case  of  abiotic  action,  as  has  been  pointed  out,  abso- 
lutely no  visible  change  either  histological  or  clinical  takes  place 
immediately  after  the  exposure,  and  usually  not  for  several  hours. 
This  is  no  doubt  due  to  the  fact  that  time  is  required  for  the  chemical 
changes  to  produce  physical  alterations.  In  the  case  of  heat  effects, 
it  is  a  matter  of  common  experience  that  latency  also  occurs  and  that 
the  time  interval  varies  with  the  intensity  of  the  exposure,  but  it  is  a 
far  less  striking  phenomenon  than  in  the  case  of  abiotic  effects.  This 
may  be  due,  among  other  causes,  to  the  fact  that  the  energy  required 
to  produce  chemical  changes  by  heat  is  so  great  owing  to  the  rapid 
dissipation  of  the  latter,  that  under  ordinary  conditions  the  critical 
point  is  quickly  passed  and  an  excessive  effect  produced. 


ABIOTIC  ENERGY  IN  THE  SOLAR  SPECTRUM. 

As  has  already  been  noted  the  solar  spectrum  when  filtered  through 
a  thick  layer  of  atmosphere  as  at  sea  level  when  the  sun  is  low  fades 
out  at  about  305  /zju.  At  high  altitudes  and  with  the  sun  running 


77 


1100 


1300/UyU 


a.  Mt.  Whitney  z.  d.  =  0° 

b.  Mt.  Whitney  z.  d.  =  60° 

FIGURE  5.     Distribution  of  energy  in  solar  spectrum. 

high,  it  extends  to  about  295  yu/z.  Under  extremely  favorable  condi- 
tions some  very  faint  traces  of  the  spectrum  were  registered  by 
Cornu  79  down  nearly  to  292  /z/z. 


706  VERHOEFF   AND   BELL. 

But  substantially  the  whole  of  the  solar  spectrum  which  is  capable 
of  producing  abiotic  action  lies  between  295  /j,/j.  and  305  nn,  is  evanescent 
under  most  conditions,  and  only  possesses  pathological  significance  at 
high  altitudes  and  especially  in  extreme  cold.  There  is  good  reason 
to  believe  that  the  atmosphere  is  considerably  more  permeable  to 
ultra  violet  radiations  at  low  temperatures  than  under  ordinary  con- 
ditions, particularly  as  regards  the  extreme  radiations.  Figure  5 
shows  from  the  data  of  Abbot  the  distribution  of  energy  in  the  so- 
lar spectrum  in  curve  (a)  at  Mt.  Whitney  for  a  zenith  distance  of  0°,  in 
curve  (b)  also  at  Mt.  Whitney  (14,000  ft.)  but  for  zenith  distance  60°. 
Near  the  latter  limit  lies  the  general  range  of  solar  radiation  as  ob- 
served at  the  surface.  Two  things  in  these  curves  are  particularly 
noteworthy,  first  that  in  both  and  especially  at  the  higher  altitude 
the  maximum  radiation  and  indeed  the  bulk  of  the  radiation  in 
general  lies  within  the  visible  spectrum.  Second,  the  maximum 
energy  lies  not  in  the  red,  but  in  the  case  of  the  high  altitude  energy 
fairly  in  the  blue  at  about  wave  length  470  ju/x  and  at  the  lower  altitude 
in  the  green  at  wave  length  about  500  /JL/JL.  So  far  as  the  solar  spec- 
trum is  concerned,  therefore,  the  heat  energy  is  chiefly  within  the 
visible  spectrum.  No  distinction  therefore  can  be  drawn  between  the 
visible  and  the  infra  red  spectrum  on  the  ground  of  heat  radiation  and 
all  attempts  to  separate  thermic  effects  by  cutting  out  the  visible 
spectrum  are  therefore  futile.  So  long  as  this  reaches  the  eye  it  carries 
with  it  the  solar  heat  in  its  greatest  intensity.  From  the  area  of  the 
curves  here  shown  it  appears  that  of  the  energy  at  high  altitudes  only 
a  very  small  proportion,  of  the  order  of  magnitude  of  one  quarter  of 
1%  lies  within  the  region  295  to  305  /zju.  Even  this  small  quantity  is 
evanescent  at  the  sea  level  and  at  ordinary  temperatures.  It  is  to  the 
small  remaining  trace  of  abiotic  rays  here  noted  that  the  phenomena 
of  snow  blindness  are  due.  From  the  clinical  standpoint  snow  blind- 
ness is  found  to  occur  only  as  a  photophthalmia  of  relatively  very  mild 
degree  and  under  exposures  usually  for  a  long  period  and  either  at 
very  high  altitudes  or  very  low  temperatures  or  with  both  these  condi- 
tions concurring.  On  snow  fields  the  exposure  of  the  eye  to  solar 
radiation,  ordinarily  greatly  ameliorated  by  the  obliquity  of  the  inci- 
dence, is  rendered  much  more  severe  by  the  reflection  from  the  snow 
which  is  a  good  reflector  down  to  the  extreme  ultra  violet  of  the  solar 
spectrum.  One  would  not  go  far  wrong  in  estimating  that  the 
radiation  reaching  the  eye  under  such  circumstances  is  of  the  order 
of  magnitude  of  a  million  ergs  per  square  cm.  per  second.  A  single 
square  meter  of  snow  at  2  meters  distance  would  reflect  to  the  eye 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          707 

almost  a  tenth  of  this  amount  with  the  altitude  and  sun  favorable. 
Assuming  now  that  one  quarter  of  1%  of  this  quantity,  that  is  250 
ergs  per  square  cm.  per  second  is  within  the  abiotic  region  295  to  305  MM 
it  is  easy  roughly  to  determine  the  exposure  which  is  likely  to  produce 
snow  blindness.  We  have  already  seen  that  a  well  marked  pho- 
tophthalmia  can  be  set  up  by  a  radiation  in  abiotic  rays  of  about 
2,000,000  erg  seconds  per  square  cm. 

Now  assuming  that  of  the  total  radiation  which  would  be  received 
direct,  half,  through  direct  and  reflected  action,  reaches  the  eye  of 
one  traveling  among  the  high  snow  fields.  The  energy  in  total  abiotic 
radiations  would  be  about  1250  ergs  per  square  cm.  per  second.  If 
all  of  this  quantity  had  the  average  abiotic  effect  on  the  conjunctiva 
and  the  cornea  a  little  less  than  27  minutes  exposure  would  be 
required  to  make  up  the  2,000,000  ergs  seconds  just  referred  to  and 
to  produce  symptoms  of  photophthalmia.  As  a  matter  of  fact 
the  region  from  305  ^  to  295  JLI/U  has  much  less  than  the  average 
abiotic  effect.  Our  crown  glass  screen  $  7  cuts  off  the  ultraviolet 
at  295juju  substantially  just  at  the  end  of  the  solar  spectrum.  Experi- 
ments made  with  this  screen  on  the  magnetite  arc  which  is  fairly 
strong  from  295  w  to  305  nn  showed  that  this  screen  increased  the 
exposure  necessary  to  produce  photophthalmia  eighteen  times.  It 
therefore  appears  that  at  a  high  altitude  in  the  snow  fields  an  exposure 
of  7  to  9  hours  under  extreme  conditions  would  be  required  to  produce 
photophthalmia  as  severe  as  that  which  we  have  here  recorded  as 
typical,  i.  e.,  involving  stippling  of  the  corneal  epithelium.  Clinically 
snow  blindness  very  rarely  reaches  this  phase,  since,  although  the 
exposures  may  be  long  the  intensity  of  abiotic  solar  radiations 
reaching  the  eye  would  be  seldom  as  great  as  the  maximum  amount 
just  mentioned.  For  instance  Schiess-Gemusens  324  reports  two  cases 
of  ordinary  snow  blindness  which  fell  under  his  own  observation 
in  which  the  ordinary  symptoms  occurred  after  practically  all  day 
exposures  showing  very  marked  conjunctivitis  without  any  visible 
effect  on  the  cornea.  Inasmuch  as  the  exposures  in  casual  climbing 
on  an  all  day  trip  are  considerably  less  severe  than  with  steady  full 
exposure  to  the  snow  fields,  it  is  fair  to  assume  that  this  latter  condi- 
tion might  produce  snow  blindness  in  perhaps  half  the  time  previously 
mentioned.  This  checks  well  writh  our  experiment  on  solar  erythema 
where  an  exposure  of  6  minutes  at  .5  meter  from  the  magnetite  arc 
unshielded  gave  a  slight  but  definite  erythema  of  the  skin.  At  sea 
level  and  under  ordinary  circumstances  the  critical  exposure  for 
snow  blindness  would  undoubtedly  run  to  many  hours.  It  is  well 


708  VERHOEFF   AND   BELL. 

known  clinically  that  snow  blindness  has  often  been  reported  in  polar 
exploration.  In  high  latitudes  at  sea  level  the  abiotic  energy  is  greatly 
reduced  but  three  circumstances  enter  the  case  to  increase  the  danger 
of  snow  blindness.  First  the  hours  of  sunlight  are  very  long,  second, 
intense  cold  is  believed  to  decrease  the  atmospheric  absorption  for 
the  extreme  ultra  violet,  and  third,  the  exposure  of  the  eye  to 
prolonged  and  intense  cold,  while  it  may  not  actually  lower  the 
vitality  of  the  cells  to  render  them  more  easily  attacked  by  abiotic 
radiation,  unquestionably  would  tend  to  lower  their  recuperative  power 
and  so  effect  the  summation  of  exposures  which  ordinarily  would  be 
relieved  by  continuous  repair. 


SOLAR  ERYTHEMA. 

These  data  on  solar  energy  at  once  call  up  the  question  of  solar 
erythema  generally  attributed  to  the  effect  of  ultra  violet  radiation.* 
Clinically  this  bears  a  suggestive  resemblance  to  photophthalmia  in 
that  it  has  a  period  of  latency  and  a  similar  period  of  duration. 
Further  it  is  well  knowTn  to  occur  easily  at  high  altitudes  with  the  sun 
running  high,  that  is  under  circumstances  which  afford  a  fair  amount 
of  abiotic  rays.  The  best  recent  investigation  of  this  matter  is  that 
by  Dr.  deLaroquette,220  Surgeon  Major  of  the  French  Army  in 
Algiers.  His  experiments  under  the  intense  tropical  sun  show  the 
connection  of  solar  erythema  with  the  abiotic  rays  very  clearly.  In 
the  first  place  in  most  cases  he  noted  a  primary  erythema  clearly 
due  to  temperature  and  perhaps  associated  with  heated  air  as  well  as 
radiation,  occurring  only  when  the  temperature  is  30  degrees  C.  or 
more.  This  is  followed  after  a  period  of  latency  of  an  hour  or  two 
by  a  secondary  photochemical  erythema  going  on  under  severe  expo- 
sures to  hemorrhagic  pigmentation,  local  oedema  and  subsequent 
desquamation.  Experiments  in  exposure  of  the  skin  under  screens 
showed  under  layers  of  quartz  and  water,  both  of  which  are  highly 
transparent  to  abiotic  rays,  the  secondary  erythema  was  well  marked. 

*  It  may  be  mentioned  here  that  there  are  certain  rare  chronic  affections  of 
the  skin,  notably  xeroderma  pigmentosa,  that  are  believed  to  be  due  to  exposure 
to  day  light,  chiefly  because  they  involve  only  the  exposed  surfaces  of  the 
body.  It  is  supposed  that  for  some  unknown  reason  the  skin  is  in  such  cases 
abnormally  sensitive  to  abiotic  radiations.  Possibly  other  slight  irritants 
applied  for  the  same  length  of  time  would  produce  similar  effects.  Two  cases 
have  been  recorded  in  which  the  cornea  was  involved,  and  one  of  us  has  per- 
sonally examined  such  a  case. 


EFFECTS   OF   RADIANT    ENERGY   ON   THE   EYE.  709 

Under  window  glass  and  violet  or  blue  glass  it  was  slight,  even  after 
considerable  exposures,  while  with  yellow,  red,  green  or  black  glass 
it  was  absent,  although  in  each  case  the  primary  erythema  was 
marked.  No  investigation  was  made  of  the  absorption  of  the  various 
glasses,  but  from  our  experiments  the  clear,  the  blue  and  the  violet 
glasses  are  likely  to  let  through  the  margin  of  the  abiotic  radiations 
in  the  thickness,  2  mm.,  here  employed.  Yellow,  red,  green  and  black 
glasses  would  certainly  cut  these  off.  The  skin  in  open  exposure  to 
sunshine  is  very  much  more  exposed  to  the  full  energy  of  the  solar 
radiations  than  is  the  surface  of  the  cornea  and  conjunctiva  and  for 
abiotic  effects  on  the  skin  practically  the  full  strength  of  solar  radia- 
tion is  available.  One  would  therefore  expect  to  get  action  from 
the  abiotic  rays  in,  at  most,  half  the  time  noted  with  respect  to  the 
cornea  and  conjunctiva  for  a  similar  degree  of  effect.  In  other  words, 
one  should  get  in  a  couple  of  hours  well  marked  effects  and  undoubtedly 
slight  erythema  in  an  hour  or  so,  as  experience  well  shows  is  the  case, 
assuming  somewhat  similar  degree  of  sensitiveness  in  the  epithelial 
cells.  In  case  of  extreme  exposure  to  heat  radiation  distinct  heat 
effects  may  be  found  in  either  case.  Dr.  deLaroquette's  observations 
on  the  human  skin  were  fully  checked  by  exposures  on  shaven  areas 
on  the  skin  of  a  guinea  pig  showing  the  same  general  phenomena. 
Dr.  deLaroquette  also  suggests  that  low  temperature  and  wind  drying 
the  epidermis  and  provoking  intense  superficial  vaso-constriction 
tends  to  exaggerate  solar  erythema.  In  this  way  some  rational 
account  can  be  given  of  its  occurrence  under  conditions  of  cold  and 
severe  wind  alone  when  the  abiotic  action  of  the  solar  radiation  would 
be  small  or  even  wanting,  in  which  case  the  effect  would  be  a  primary 
rather  than  a  secondary  one.  Finally,  in  solar  erythema,  as  in  pho- 
tophthalmia,  repeated  exposures  of  somewhat  subnormal  intensity 
give  acquired  tolerance,  wThile  the  skin  is,  as  well  known,  somewhat 
hypersensitive  to  severe  exposures  following  each  other  without 
time  for  the  lesions  to  undergo  repair. 

Our  experiments  with  the  bare  magnetite  arc  as  source  indicate 
that  the  liminal  exposure  for  perceptible  abiotic  effects  is  practically 
the  same  for  the  more  sensitive  parts  of  the  skin  as  for  the  conjunctiva. 
The  inner  portion  of  the  forearm  was  the  portion  of  the  body  exposed 
in  our  work  on  liminal  exposures.  Here  with  6  minutes  at  .5  meter, 
which  corresponds  very  well  with  the  production  of  mild  photoph- 
thalmia,  a  slight  reddening  of  the  skin  appeared  some  few  hours 
after  exposure,  rose  to  its  maximum  inside  of  the  first  24  hours  and 
vanished  within  a  day  or  two  leaving  no  trace.  Through  the  double 


710  VERHOEFF   AND   BELL. 

lens  system  and  crown  glass  screen  (295  jtiju)  already  described,  the  lim- 
inal  exposure  was  between  15  and  30  seconds,  the  former  figure  giving 
no  traces  and  the  latter  slightly  more  than  a  liminal  exposure.  In  all 
exposures  over  half  a  minute  there  was  immediate  heat  erythema 
and  a  subsequent  development  after  a  period  of  latency  of  a  few 
hours.  There  was  a  distinct  but  slight  feeling  of  heat  during  the 
exposure  and  a  rather  rapid  extension  of  the  erythema  somewhat 
beyond  the  limits  of  the  5  mm.  stop  which  limited  the  area  exposed. 
In  cases  of  severe  exposure  to  the  sun  we  are  inclined  to  think  that 
this  primary  erythema  due  purely  to  the  effects  of  heat  is  of  consider- 
able importance  in  the  total  results  experienced.  We  found,  as  did 
Dr.  deLaroquette,  that  vaseline  acted  as  a  fairly  complete  preventive 
as  regards  both  primary  and  secondary  erythema,  particularly  the 
latter,  while  glycerine  gave  a  slight  protective  action  in  our  results, 
more  than  would  seem  to  be  warranted  in  view  merely  of  its  trans- 
parency to  abiotic  rays.  From  these  observations  and  from  the 
clinical  facts,  often  showing  erythema  greatly  disproportionate  to 
the  intensity  of  abiotic  radiation  likely  to  be  present,  it  seems  prob- 
able that  ordinary  sunburn  is  due  to  a  mixture  of  thermic  and  abiotic 
effects  of  which  the  former  are  often  the  more  prominent,  although 
they  generally  cannot  readily  be  separated  from  the  secondary  abio- 
tic effects,  the  development  of  which  they  tend  to  mask. 


ERYTHROPSIA. 

So-called  erythropsia  is  the  name  of  a  phenomenon  rather  than  of 
a  pathological  condition.  The  clinical  records  are  numerous  but 
vague.  They  all  indicate  a  condition,  generally  very  temporary, 
in  which  the  patient  finds  a  more  or  less  ruddy  tinge  in  everything 
seen.  There  is  nothing  definite  in  the  tint  of  the  coloration  or  the 
period  through  which  it  is  observable.  It  apparently  runs  from  vari- 
ous shades  of  orange  and  rose  to  a  fairly  full  red.  The  most  definite 
description  given  of  the  apparent  color,  which  evidently  pertains  to  a 
rather  extreme  incidence,  is  given  by  Fuchs  126,  who  compares  it  to  a 
strong  fuchsin  solution  with  a  trace  of  eosin  solution.  A  cursory  view 
of  the  clinical  records  indicates  that  the  cases  cited  fall  into  three 
general  divisions.  First,  cases  associated  with  neurosis  such  as  those 
given  by  Charcot  and  others  (cited  by  Wyeller422).  These  clearly 
•cannot  be  associated  with  any  pathological  condition  of  the  visual 


EFFECTS    OF   RADIANT    ENERGY    ON   THE    EYE.  711 

apparatus.  Second,  there  are  many  recorded  instances  of  traumatic 
erythropsia  some  of  which  at  least  evidently  are  associated  with 
the  actual  infiltration  of  the  eye  media  with  blood.  Third,  one  finds 
a  vast  majority  of  instances  which  one  may  term  photo-erythropsia 
in  which  the  observed  appearances,  one  can  hardly  dignify  them  by 
the  name  of  symptoms,  are  associated  with  over  exposure  to  light. 
These  are  so  entirely  without  pathological  significance  that  we  should 
hardly  consider  them  here  save  for  the  fact  that  the  phenomena  have 
been  by  some  writers  like  Widmark  411,  Fuchs  126,  and  others,  subse- 
quently attributed  to  the  effect  of  ultra  violet  radiations.  As  this 
erroneous  conception  of  the  fact  still  persists  in  spite  of  the  admirable 
work  of  Vogt,402  it  is  desirable  here  to  note  the  relation  of  this  so-called 
erythropsia  to  the  general  phenomenon  of  color  vision.  The  whole 
subject  was  'thoroughly  investigated  recently  by  Wydler  422  who  very 
plainly  showed  that  erythropsia  is  due  to  the  red  phase  of  the  negative 
after  image  following  over-exposure  to  light,  ordinarily  brilliant  white 
light,  although  green  and  blue  green  illumination  is  even  more  effective. 
The  association  of  the  phenomenon  with  ultra  violet  radiation  appears 
to  be  due  to  the  fact, that  photo-erythropsia  has  been  often  observed 
after  the  intense  glare  which  produces  snow  blindness  and  not  infre- 
quently in  the  aphakic  eye  after  an  operation  for  cataract.  That  the 
ultra  violet  really  has  nothing  to  do  with  the  matter  is  clearly  shown 
by  Vogt 402  who  found  that  erythropsia  could  not  be  produced  experi- 
mentally by  the  ultra  violet  rays  alone,  but  very  easily  by  light  rays 
containing  no  ultra  violet.  We  need  only  add  here  that  it  is  possible 
to  produce  marked  erythropsia  through  euphos  glass  which  transmits 
no  ultra  violet,  through  B-naphthol-disulphonic  acid  which  also  cuts 
off  the  ultra  violet,  and  through  dense  flint  glasses  which  eliminate 
all  of  the  ultra  violet  which  could  with  any  certainty  get  through  the 
lens.  Also  it  is  produced  with  great  facility  by  radiation  through 
green  and  blue  green  media  which  intercept  the  ultra  violet  com- 
pletely, but  flood  the  eye  with  light  of  a  color  certain  to  produce  a 
strong  red  phase  in  the  after  image.  The  truth  seems  to  be  that  the 
so-called  photoerythropsia  is  merely  the  result  of  such  unequal  fatigue 
of  the  primary  color  sensations  as  leaves  for  a  greater  or  less  time  there- 
after a  color  sensation  predominantly  red.  This  conception  clears 
up  at  once  the  difficulty  of  accounting  for  the  partial  erythropsia 
which  has  been  noted  by  Purtscher  287  and  others,  since  in  cases  of 
unequal  exposure  of  various  parts  of  the  retina  to  brilliant  light  the 
fatigue  effects  necessarily  must  vary  over  the  field  of  vision.  A  glance 
at  figure  (6)  will  render  the  situation  clear.  The  curves  in  this  figure 


712 


VERHOEFF   AND   BELL. 


rare  those  of  the  three  normal  color  sensations  reduced  to  equal  areas 
as  determined  by  Exner.  If  any  of  these  primary  sensations  are 
fatigued  that  of  the  remaining  color  or  colors  becomes  the  predomi- 
nant tint  seen.  This  has  been  beautifully  shown  by  Burch  who  by 
suitable  means  fatigued  to  complete  exhaustion  each  one  of  the  sen- 
sations and  various  combinations  of  them.  Burch  61  found  that  of 
the  three  the  red  first  regained  its  sensibility,  after  perhaps  ten  min- 
utes, followed  by  the  green  and  last  of  all  by  the  blue  where  marked 
fatigue  might  persist  for  several  hours.  Red  vision  is  therefore 
normally  to  be  expected  after  fatigue  of  all  three  sensations  since  the 
red  recovers  first  and  in  case  the  green  and  blue  are  more  fatigued  than 
the  red  the  latter  will  be  more  notably  predominant.  As  the  maxi- 
mum luminosity  of  the  spectrum  lies  in  the  green  and  as  at  high  alti- 
tudes under  a  clear  sky  the  blue  is  relatively  strong,  exposure  in  the 


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Wave  length 
FIGURE  6.     Primary  color  sensations,  after  Exner. 

high  snow  fields  necessarily  fatigues  these  two  sensations  predomi- 
nantly, and  photoerythropsia  in  greater  or  less  degree  may  reasonably 
be  expected. 

As  a  corollary  we  may  note  the  reputed  activity  of  the  quartz  mer- 
cury arc  in  producing  erythropsia.  On  figure  2,  Plate  5,  marked  in 
their  proper  positions  are  the  three  chief  lines  of  the  mercury  spectrum 
at  waves  lengths  454:  /JL/JL,  546  H/JL,  and  the  pair  at  578  /JL/JL.  It  will  be 
seen  that  they  lie  in  positions  which  indicate  stronger  fatigue  of  the 
green  than  of  the  red  and  marked  fatigue  in  the  blue.  The  green  line 
at  546  nn  is  by  far  the  strongest  of  the  three  followed  by  the  yellow 
pair  at  578  HP  and  by  the  strong  line  of  blue.  The  chief  red  line  in  the 
spectrum  is  relatively  very  weak  hence  fatigue  weakens  the  green  most, 
red  in  the  next  degree  and  blue  relatively  little.  After  fatigue, 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         713 

therefore,  the  red  comes  easily  and  quickly  into  activity  and  unites 
with  the  residual  blue  to  produce  very  marked  erythropsia  of  a  dis- 
tinctly rosy  tinge.  This  lasts  for  some  minutes,  while  traces  of  the 
disturbance  of  the  blue  and  green  vision  may  still  be  found  after  pro- 
longed exposure  for  a  period  of  several  hours,  and  this  like  other  forms 
of  color  fatigue  takes  place  whenever  the  light  which  affects  the  three 
primary  sensations  has  been  active,  quite  irrespective  of  whether 
the  ultra  violet  is  present  or  absent. 

As  to  the  aphakic  eye  Wydler  422  has  noted  the  probable  effect  of 
coloration  of  the  lens  in  this  connection.  When  an  eye  has  been 
shielded,  often  for  years,  against  any  strong  access  of  the  blue  and 
violet  and  against  the  extreme  end  of  the  green  sensation  as  well  and 
is  then  after  recovery  from  cataract  operation  exposed  to  strong  day- 
light, it  is  merely  a  phenomenon  to  be  expected  if  there  is  predominant 
red  vision  after  fatigue.  It  would  not  be  surprising,  for  that  matter, 
if  after  long  disuse  of  the  color  sensations  toward  the  blue  end  of  the 
spectrum  fatigue  were  easier  and  recovery  less  prompt  than  in  the 
normal  eye.  Aphakic  patients  in  whom  the  pupil  is  often  greatly 
enlarged  as  a  result  of  iridectomy  are  likely  to  receive  extraordinarily 
intense  illumination  on  the  retina,  and  hence  may  show  the  phenome- 
non of  color  fatigue  to  an  exceptionally  great  extent.  Exposed  in  the 
open  the  color  fatigue  is  very  marked,  and  when  this  wears  off  after 
the  exposure  ceases,  the  return  of  the  red  sensation  may  very  naturally 
be  accompanied  by  some  degree  of  erythropsia  for  this  reason  alone. 
One  of  us  has  recently  examined  a  case  in  which  erythropsia  so  pro- 
duced was  a  characterisitc  condition. 


VERNAL  CATARRH. 

Spring  catarrh  is  an  uncommon  disease  of  the  conjunctiva  that 
most  often  affects  the  upper  lid,  much  less  often  the  bulbar  conjunc- 
tiva around  the  corneal  limbus,  and  almost  never  the  two  together. 
It  is  extremely  chronic,  lasting  from  3  to  20  years,  and  is  associated 
with  the  formation  of  peculiar  granulation  tissue,  infiltrated  with 
eosinophilic  leucocytes  to  an  unusual  degree,  containing  downgrowths 
of  epithelium  from  the  surface.  In  the  case  of  the  conjunctiva  of 
the  lid,  the  new  tissue  forms  within  the  papillae,  thus  giving  rise  to 
large  flat  papillary  growths.  The  symptoms  of  irritation,  photophobia, 
lacrimation,  and  itching,  are  most  marked  in  the  spring  and  warm 


/14  VERHOEFF   AND    BELL. 

seasons  of  the  year,  usually  disappearing  during  the  winter  months. 
For  this  reason  sunlight  has  been  suggested  as  the  etiological  factor 
in  the  disease. 

This  hypothesis  was  first  advanced  by  Schiele  323  and  advocated 
by  Kreibich  211  who  showed  that  an  occlusive  bandage  had  a  favorable 
effect  upon  the  symptoms.  This  effect,  however,  may  be  explained 
in  other  ways  than  by  the  shutting  out  of  light.  Birch-Hirschfeld  34 
repeatedly  exposed  the  conjunctiva  of  a  rabbit  within  a  period  of 
18  months  to  the  "Uviol  lampe"  of  Schott  and  obtained  changes 
stated  to  be  not  unlike  those  of  vernal  catarrh.  He  does  not,  however, 
accept  the  view  that  the  latter  is  due  to  ultra  violet  light.  No  doubt 
similar  changes  could  be  produced  by  other  irritants  frequently 
applied. 

The  evidence  for  the  view  that  vernal  catarrh  is  due  to  the  action 
of  sunlight,  therefore  amounts  to  little  more  than  the  fact  that  the 
symptoms  are  most  pronounced  in  the  spring  and  summer.  This 
fact,  however,  is  accounted  for  even  better  on  the  more  recent  theory 
that  the  disease  is  due  to  pollen.  Moreover  the  following  objections, 
that  to  us  seem  insurmountable,  may  be  urged  against  sunlight  as  a 
cause.  In  the  first  place  if  vernal  catarrh  is  due  to  sunlight  the  lower 
lid,  which  is  not  only  more  exposed,  but  thinner  and  more  trans- 
parent, should  be  more  affected  than  the  upper  lid,  whereas,  as  a 
matter  of  fact,  it  entirely  escapes  involvement.  In  this  connection 
it  may  be  noted  that  in  cases  of  trachoma,  a  somewhat  similar  disease, 
the  lower  lid  also  usually  escapes  and  here  the  disease  is  undoubtedly 
due  to  some  infectious  agent.  Similarly  this  theory  is  inconsistent 
with  the  fact  that  the  bulbar  conjunctiva,  which  is  directly  exposed 
to  the  light,  is  but  seldom  affected,  and  almost  never  affected  in  associ- 
ation with  the  palpebral  form  of  the  disease. 

Finally,  the  possibility  of  abiotic  action  is  ruled  out  by  the  fact 
that  it  is  impossible  for  abiotic  waves  to  pass  through  the  entire 
thickness  of  the  lid,  if  only  on  account  of  its  rich  vascularization. 
This  objection  does  not  apply  to  possible  heat  effects  produced  by 
visible  or  infrared  rays,  but  in  this  case  it  would  be  necessary  to 
assume  exposure  of  the  eyelid  to  direct  sunlight  for  considerable 
periods  of  time  as  well  as  special  sensitiveness  of  the  conjunctiva  to 
heat,  neither  of  which  conditions  seems  possible. 


EFFECTS   OF    RADIANT    ENERGY   ON    THE    EYE.  715 


SENILE  CATARACT. 

The  theory  has  been  advanced  (see  page  780)  that  senile  cataract 
is  due  to  exposure  of  the  lens  to  daylight,  particularly  that  from  the 
sky.  This  is  based  solely  on  the  fact  that  the  cataractous  changes 
usually  begin  in  the  lower  part  of  the  lens.  It  is  undoubtedly  true 
that  the  changes  do  first  appear  below,  but  as  a  rule  they  are  so  far 
below  that  they  are  in  a  portion  of  the  lens  completely  shaded  by  the 
iris.  Thus  it  is  most  often  necessary  to  produce  artificial  mydriasis 
before  incipient  lens  changes  can  be  seen  with  the  ophthalmoscope. 
Moreover,  if  the  cataract  were  due  to  exposure  to  light,  the  pupillary 
area  should  be  the  first  affected,  since  from  such  an  extended  source 
as  the  sky  it  receives  the  greatest  concentration  of  light,  and  since 
the  chief  absorption  must  occur  here.  We  must  conclude,  therefore, 
that  there  is  no  sound  evidence  for  this  theory  of  cataract  formation. 

A  possible  explanation  of  the  fact  that  the  lower  part  of  the  lens 
is  usually  first  affected  in  senile  cataract  is  that  the  structure  of  the 
lens  may  normally  be  slightly  different  here  than  elsewhere.  From  a 
developmental  standpoint  this  is  indicated  by  the  fact  that  coloboma 
of  the  lens  usually  occurs  below.  Burge  61a  has  recently  attempted 
to  supply  an  experimental  basis  for  the  view  that  ultra  violet  light  is 
responsible  for  cataract.  He  found  that  the  rays  from  an  unscreened 
quartz  mercury  vapor  lamp  had  almost  no  coagulating  effect  upon 
the  lens  protein  even  after  an  exposure  of  72  hours  at  a  distance 
of  5  cm.  but  that  when  acting  in  the  presence  of  weak  solutions  of 
calcium  chloride,  sodium  silicate,  or  dextrose,  coagulation  occurred. 
Since  in  senile  cataracts  calcium,  magnesium,  and  sometimes  silicates, 
are  greatly  increased,  and  in  diabetic  cataracts  dextrose  is  presum- 
ably present,  Burge  assumes  that  these  cataracts  are  due  to  the  action 
of  ultra  violet  light.  That  is,  he  assumes  that  these  substance  are 
present  in  undue  quantities  in  the  lenses  of  certain  individuals  and 
that  this  renders  their  lenses  vulnerable  to  the  short  waves  of  daylight. 

This  assumption  is  sufficiently  controverted  by  the  fact  just  men- 
tioned that  senile  cataract  usually  begins  at  the  periphery  below. 
But  in  addition,  other  serious  objections  to  his  argument  may  be 
pointed  out.  In  the  first  place,  in  traumatic  cataracts  and  cataracts 
clue  to  inflammatory  conditions,  calcium  salts,  and  no  doubt  mag- 
nesium and  other  salts,  are  deposited  in  great  abundance,  and  the 
lens  may  even  become  completely  calcified.  In  fact,  the  same  thing 
occurs  in  dead  tissues  anywhere  in  the  body,  so  that  the  reasonable 


716  VERHOEFF   AND   BELL. 

assumption  is  that  the  presence  of  these  salts  in  senile  cataract  is  a 
result  not  a  cause.  Then,  too,  Burge  made  use  of  intensities  of  expo- 
sure and  wave  lengths  to  which  the  lens  is  never  subjected  during  life. 
The  cornea  completely  screens  it  from  practically  all  the  short  waves 
found  effective  by  him.  The  longest  waves  with  which  he  could 
coagulate  proteins  were  302  /JL/JL  in  length  and  the  effect  produced  by 
these  was  insignificant. 

Burge  suggested  also  that  his  results  might  apply  to  glassblowers 
cataract,  overlooking  the  fact  that  the  latter  typically  begins  at  the 
posterior  pole  of  the  lens,  whereas  in  his  experiments  the  part  of  the 
lens  away  from  the  light  was  little  if  at  all  affected.  It  is  of  course 
obvious  that  the  slight  loss  of  transparency  he  sometimes  observed 
in  this  part  of  the  lens  could  not  have  been  due  to  the  direct  action 
of  the  light,  since  the  effective  rays  could  not  have  penetrated  so  far. 
The  fatal  objection  to  Burge's  theory  as  applied  to  senile  cataract  is 
that  the  ultra  violet  solar  rays  cannot  reach  that  portion  of  the  lens 
where  cataract  generally  begins,  and  that  portion  of  the  lens  where 
ultraviolet  light  has  the  best  chance  of  action  is  affected  only  at  a 
late  stage  of  development. 


CONCENTRATION  OF  ENERGY  IN  IMAGES. 

We  have  already  shown  that  superficial  action  of  radiant  energy 
on  the  eye  depends  on  the  actual  energy  in  ergs  per  square  cm.,  or 
other  convenient  measure,  which  falls  upon  the  surface.  Such  value 
is  directly  as  the  energy  of  the  source  and  inversely  as  the  square  of 
its  distance.  The  density  of  incidence  of  energy  at  points  within  the 
eye  is  obviously  dependent  on  the  amount  to  which  the  superficial 
energy  is  concentrated  by  the  refracting  media,  and  at  the  retina  the 
concentration  of  energy  is  determined  by  the  size  of  the  image  and  the 
aperture  of  the  refracting  system,  which  is  determined  by  the  area 
of  the  pupil.  In  dealing  with  an  extended  source  the  image  is  corre- 
spondingly extended  and  the  surface  density  of  energy  in  the  image 
is  correspondingly  reduced.  Hence  it  is  that  with  sources  like  the 
tube  of  the  quartz  arc  the  image  density  is  relatively  small,  while 
with  point  sources  or  those  of  very  small  area,  like  the  electric  arc, 
the  retinal  area  is  correspondingly  small  and  of  the  total  energy  reach- 
ing the  pupil  there  is  a  greater  concentration  in  the  image.  Within 
limits  the  intensity  of  the  effect  on  the  retina  is  then  directly  pro- 
portional to  the  intrinsic  brilliancy,  or  radiation  per  unit  area  of  the 


EFFECTS   OF   RADIANT    ENERGY   ON   THE    EYE.  717 

source.  The  mere  lowering  of  the  intrinsic  radiation  by  spreading 
out  the  source  therefore  greatly  lessens  any  possible  effects  of  energy 
which  may  reach  the  retina,  while  it  does  not  in  any  way  affect  the 
radiation  which  may  reach  the  cornea  and  conjunctiva.  There  is, 
however,  a  very  notable  limitation  to  this  principle  which  comes 
into  play  in  considering  small  and  intense  radiants,  as  was  long  ago 
shown  by  Charpentier  69.  When  the  image  of  a  luminous  object 
reaches  the  diameter  of  approximately  0.15  mm.,  variations  of  intrin- 
sic radiation  at  the  source  cease  to  be  significant  and  the  appar- 
ent intensity  of  the  source  varies  simply  with  the  inverse  square  of  its 
distance.  This  corresponds  to  the  visual  angle  of  about  40  minutes 
of  arc.  For  areas  of  greater  dimensions  one  must  reckon  with  the 
size  of  the  image  as  determined  by  the  ordinary  laws  of  geometric 
optics,  but  for  radiants  of  less  than  this  dimension  the  image  may  be 
taken  as  of  constant  area  corresponding  to  the  circle  of  diffusion,  and 
the  energy  concentrated  in  it  varies  as  the  inverse  square  of  the 
distance  of  the  radiating  source.  In  any  case  the  energy  reaching  the 
retina  is  diminished  by  the  absorption  in  the  media  of  the  eye  of  which 
we  will  now  take  account. 


GENERAL  NATURE  OF  ABSORPTION. 

By  absorption  one  means  in  general  terms  the  stoppage  of  energy 
in  any  medium.  This  may  be  either  specific,  affecting  only  energy  of 
certain  wave  length,  or  general,  affecting  more  or  less  all  energy  what- 
ever. In  the  former  case  it  is  due  to  the  molecular  or  atomic  struc- 
ture of  the  material,  in  the  latter  to  the  fact  that  it  is  not  physically 
homogeneous.  In  specific  absorption  such  as  takes  place,  for 
instance,  in  colored  glasses,  the  molecular  structure  is  such  as  to 
respond  to  and  take  up  certain  particular  oscillation  frequencies  so 
that  waves  of  these  frequencies  do  not  readily  pass  through  the  sub- 
stance. In  general  absorption  the  substance  contains  particles  which 
reflect  the  energy  from  their  surface  or  absorb  it  without  definite 
regard  to  its  wave  length.  Such  absorption  occurs,  for  instance, 
in  some  glass  which  is  full  of  microscopic  bubbles  which  reflect  the 
energy  at  their  surfaces,  or  in  certain  dark  glasses  which  are  filled  with 
minute  opaque  particles.  Both  kinds  of  absorption  may  coexist  in 
the  same  material,  but  general  absorption  involves  it  only  in  a  very 
indirect  way  due  to  the  general  properties  of  reflecting  surfaces. 

The  stoppage  of  radiant  energy  in  the  media  of  the  eye  is  of  two 


718  VERHOEFF  AND   BELL. 

kinds.  First,  by  absorption  in  the  ordinary  sense,  and  second,  by 
reflection  due  to  the  structure  of  the  eye.  For  instance,  the  cornea  is 
somewhat  lamellar  in  structure,  built  up  of  successive  layers  and  cells 
and  is  therefore,  owing  to  the  differences  in  the  index  of  refraction  as 
the  ray  traverses  the  structure,  somewhat  less  transparent  than  if  it 
were  homogeneous.  There  is  also  a  slight  loss  of  energy  at  the  surface 
in  passing  into  the  aqueous.  This  is  also  practically  homogeneous, 
but  there  is  again  a  slight  loss  by  reflection  in  passage  from  the  aque- 
ous to  the  lens  which  has  a  materially  higher  index  of  refraction, 
and  is  of  itself  non  homogeneous  from  the  standpoint  of  refraction. 
Finally  there  is  reflection  passing  from  the  lens  into  the  vitreous  and 
the  vitreous  itself  is  not  without  structure,  so  that  in  fact  the  path 
of  rays  through  it  can  be  traced  by  the  faint  diffused  illumination  due 
to  its  lack  of  homogeneity.  It  is  quite  impossible  to  determine  accu- 
rately these  losses,  except  for  the  initial  loss  which  occurs  by  reflection 
at  the  surface  of  the  cornea  to  which  we  have  already  drawn  attention. 
These  losses  are  greater  for  rays  of  short  wave  length  than  for  those  of 
long,  and  perhaps  the  most  that  can  be  said  about  them  numerically 
is  that  a  total  loss  is  probably  of  the  order  of  magnitude  of  10%  for 
rays  of  medium  wave  length. 

The  general  absorption  of  the  media  of  the  eye  has  been  studied 
by  Aschkinass5  in  connection  with  his  determination  of  the  absorp- 
tion spectrum  of  fluid  water.  He  found  that  the  transmission  of  the 
media  of  the  eye  for  radiant  energy  in  general  was  closely  similar 
to  that  of  water  in  a  layer  of  equal  thickness.  The  large  proportion 
of  water  in  these  media  would,  of  course,  suggest  a  similarity  and 
Aschkinass  found  the  characteristic  absorption  bands  of  water  in  the 
experiments  on  the  eyes  of  cattle  and  some  control  experiments  on 
the  human  eye.  The  only  notable  discrepancy  was  in  finding  a  con- 
siderably higher  absorption  in  the  cornea  than  would  be  warranted 
by  its  water  equivalent  which  Aschkinass  describes  chiefly  to  a  film 
forming  very  rapidly  over  the  surface  of  the  dead  cornea.  In  examin- 
ing the  bearing  of  these  facts  on  the  energy  focussed  upon  the  retina 
in  any  given  case  it  should  be  noted  that  the  absorption  is  chiefly 
in  the  infra  red.  Figure  7  shows  the  absorption  curve  of  a  5cm  layer  of 
water  as  found  by  Aschkinass  5.  Hence  in  examining  the  absorption 
in  any  given  source  of  energy  it  will  be  found  relatively  greatest  for 
infra  red  radiation,  except  for  the  effect  of  the  lens  in  cutting  off  a 
large  part  of  the  ultra  violet.  Luckiesh  23°  has  made  a  study  of  the 
absorption  of  energy  from  various  sources  by  the  eye,  based  on  Asch- 
kinass's  results.  From  this  it  appears  that  from  low  temperature 


EFFECTS   OF    RADIANT    ENERGY    ON   THE    EYE. 


719 


sources  like  carbon  incandescent  lamps  and  ordinary  flames  the 
absorption  of  the  total  energy  rises  to  nearly  90%.  As  we  have 
already  shown  this  must  be  increased  by  miscellaneous  losses  by 
reflection  so  that  the  amount  of  energy  actually  available  in  the 
image  on  the  retina  from  such  sources  is  very  small.  It  is  quite 
otherwise  with  radiants  like  the  sun,  which  is  roughly  equivalent 
to  a  body  of  5,500  to  6,500  degrees  absolute  as  regards  the  char- 
acter of  its  radiation.  From  such  a  source  the  specific  absorp- 
tion of  water  cuts  off  relatively  little,  and  the  total  loss  of  energy 


s§ 

o 

1 

g 

£ 


.8       .9       1.0      1.1      1.2      1.3      1.4      1.5/1 


Wave  length 
FIGURE  7.     Approximate  absorption  of  5cm  water,  from  data  of  Aschkinass. 

in  the  eye  is  of  the  order  of  magnitude  of  25  to  30%.  In  phenomena 
like  eclipse  blindness  therefore  not  only  is  the  eye  exposed  to  a 
very  powerful  radiating  source,  but  the  radiation  is  of  such  char- 
acter that  it  is  not  strongly  absorbed  and  hence  the  energy  in  the 
image  may  rise  to  very  great  intensity.  The  solar  radiation  curves 
already  shown  make  it  plain  that  the  proportion  of  energy  cut  off 
will  be  greater  the  greater  the  altitude  of  the  sun  and  the  less  the 
general  atmospheric  absorption.  Taking  30%  as  the  total  cut  off 
in  the  eye  one  may  obtain  an  approximate  idea  of  the  energy  concen- 
trated on  the  retina  in  observing  the  sun  unscreened,  the  total  radia- 
tion being  about  106  ergs  per  square  cm.  per  second;  and  assuming 
the  pupillary  diameter  to  be  about  2  mm.,  approximately  3%  of  this 
energy  will  enter  the  eye,  and  subtracting  30%  for  absorption  and 
reflection  it  results  that  the  total  energy  concentrated  in  the  image 
would  be  about  20,000  ergs  per  second.  Taking  the  area  affected 
as  approximately  .15  mm.  in  diameter  the  concentration  of  energy 
in  the  image  is  on  the  basis  of  nearly  113  X  106  ergs  per  square  cm. 
per  second.  Even  if  only  a  quarter  or  a  half  of  this  amount  is  avail- 
able in  the  case  of  the  partially  eclipsed  sun,  it  is  evident  that  the 
immense  concentration  of  energy  in  the  image  is  sufficient  to  produce 


720  VERHOEFF   AND   BELL. 

destructive  effects  such  as  have  been  often  clinically  noted  and  which 
we  have  observed  in  our  experiments.  From  the  relatively  small 
absorption  by  the  eye  media  in  the  case  of  solar  radiation  it  is  clear, 
however,  that  it  is  far  more  dangerous,  in  proportion  to  its  intensity, 
than  any  artificial  source  of  radiation. 

Passing  from  the  general  absorption  of  the  eye  for  radiant  energy 
here  considered  to  the  specific  absorption  of  the  several  media,  the 
facts  have  been  pretty  thoroughly  established  by  the  researches  of 
Hallauer152,  Schans  and  Stockhausen312  and  Martin238.  As  regards 
the  general  volume  of  radiant  energy  received  by  the  eye  there  is  no 
specific  absorption  except  that  already  noted  due  to  the  aqueous 
content.  Aside  from  this  the  numerical  proportion  of  the  energy  from 
most  sources  specifically  absorbed  in  the  eye  is  very  small  and  is  con- 
fined to  the  ultra  violet  region.  The  human  cornea  cuts  off  practi- 
cally all  the  energy  of  wave  length  less  than  295  H/JL.  The  lens  wipes 
out  the  remaining  ultra  violet  up  to  a  point  between  380  IJL/J,  and  400  IJL/JL. 
The  vitreous  absorbs  strongly  in  the  general  region  between  250  ju^ii 
and  300  IJ./JL  in  the  thickness  in  which  it  exists  in  the  human  eye.  Only 
a  very  minute  proportion  of  energy  within  this  range  gets  through  so 
that  the  general  effect  of  the  absorption  in  the  vitreous  in  the  case  of 
an  aphakic  eye  is  to  re-enforce  that  of  the  cornea,  as  is  well  shown  by 
the  immunity  from  abiotic  action  of  the  retina  in  our  experiment  No. 
89.  In  his  experiment  on  the  eye  of  a  young  rabbit,  Martin  found  the 
limits  of  transmission  to  be  about  those  here  noted,  except  that  the 
lens  transmitted  freely  radiations  longer  than  350  juju.  As  the  human 
lens  yellows  with  age  its  absorption  reaches  down  into  the  violet, 
extending  even  to  420  ju^. 


ECLIPSE  BLINDNESS  AND  ALLIED  PHENOMENA. 

Every  recent  eclipse  of  the  sun  has  given  rise  to  numerous  cases 
of  so-called  eclipse  blindness,  due  to  careless  observation  of  the  phe- 
nomenon in  its  partial  stages,  either  with  the  naked  eye  or  with 
altogether  insufficient  protection.  We  should  not  here  consider  the 
matter  worthy  of  attention  were  it  not  for  the  fact  that  it  has  been 
loosely  ascribed,  like  many  other  imperfectly  investigated  ocular 
injuries,  to  the  malign  effects  of  ultra  violet  light.  Eclipse  blindness 
appears  in  literature  as  far  back  as  Plato's  Phaedo,  and  is  repeatedly 
mentioned  through  classical  and  post  classical  times  as  an  appar- 
ently not  unexpected  phenomenon.  The  eclipse  of  April  17,  1912,  in 


EFFECTS   OF   RADIANT   ENERGY   ON   THE  EYE.  721 

Germany  produced  a  total  of  many  hundred  cases  of  more  or  less  in- 
jury to  the  eyes,  as  noted  by  Wendenberg  41°.  Every  eye  clinic  re- 
ceived its  toll  of  more  or  less  severe  cases.  Clinically  the  immediate 
effect  is  marked  and  immediate  scotoma,  which  does  not  pass  away 
promptly  but  leaves  more  or  less  serious  cloudiness  of  vision  and 
accompanying  loss  of  acuity  which  may  be  temporary,  lasting  a  few 
weeks,  or  in  severe  cases  permanent.  The  scotoma  is  commonly 
central  and  generally  of  small  extent,  in  a  marked  proportion  of  the 
cases  corresponding  fairly  well  with  the  dimensions  of  the  sun's  image, 
although  wide  variations  from  this  may  be  due  to  repeated  fixations 
overlapping  or  reenforcing  each  other.  As  it  is  generally  impossible 
to  tell  just  how  long  or  how  often  the  patient  fixed  the  phenomenon 
nothing  definite  can  be  postulated  concerning  various  varieties  of 
scotoma  which  have  been  noted  by  various  observers.  The  ophthal- 
moscopic  observations  usually  show  changes  ranging  from  scarcely 
perceptible,  to  conspicuous  and  permanent  pathological  appearances 
involving  lasting  and  destructive  injury  to  the  retina.  Metamorphop- 
sia  sometimes  appears,  the  significance  of  which  will  be  apparent  in 
connection  with  some  of  our  experiments,  and  diminution  of  visual 
acuity  is  fairly  well  marked,  often  falling  below  one  third.  With  the 
progress  of  time  the  scotoma  tends  to  contract  and  in  mild  cases 
normal  vision  is  regained  within  some  weeks,  or  in  the  most  severe 
cases  great  reduction  in  acuity  persists  permanently.* 

Our  experiments  have  been  directed  to  the  production  of  an  artificial 
eclipse  blindness  in  animals,  and  the  examination  of  the  lesions  pro- 
duced, following  up  the  wrork  of  Czerny  85,  Deutschman  89,  Herzog 176, 
and  others  with  special  reference  to  the  intensity  required  to  produce 
the  lesions  noted.  The  character  of  the  lesions  produced  in  these 
experiments  is  described  elsewhere  (page  697).  The  apparatus  em- 
ployed was  powerful  enough  to  produce  prompt  and  acute  effects. 
For  most  of  the  experiment  we  employed  the  mirror  apparatus  shown 
in  Plate  8  which  consisted  of  a  silvered  glass  mirror  26  cm.  in  diameter 
and  1.5  meters  focal  length,  carried,  as  shown,  in  a  fork  mounting  set 
up  approximately  in  the  meridian  and  fitted  with  slow  motions  in 
right  ascension  and  declination  so  that  the  beam  could  be  readily 

*  Jess  2 00  describes  relative  ring  scotoma  for  colors  in  a  series  of  cases,  but 
does  not  offer  a  convincing  explanation  for  its  occurrence.  Boehm*8  was  un- 
able to  demonstrate  it  in  any  of  his  cases,  although  he  examined  them  with 
special  reference  to  it.  Birch-Hirschf  eld  41  suggests  that  a  normal  eye  would 
show  the  same  condition  if  examined  in  the  same  way.  This  criticism  would 
seem  to  apply  with  equal  force  to  the  similar  scotomata  reported  by  Birch- 
Hirschfeld35  himself  as  occurring  after  exposure  to  ultra  violet  light. 


722  VERHOEFF   AND   BELL. 

directed  and  kept  in  position.  In  use  the  mirror  was  slightly  tilted 
so  as  to  throw  the  focus  just  out  of  the  path  of  the  direct  incident 
beam.  The  concentration  of  energy  obtained  by  this  instrument  was 
enormously  great,  owing  to  the  size  of  the  mirror  and  its  relatively 
short  focal  length.  Its  area  was  about  530  square  cm.  so  that  with 
an  average  reflective  coefficient  of  0.75,  with  good  sunlight  the  re- 
flected energy  would  amount  to  some  4  X  108  ergs  per  second.  The 
image  of  the  sun  formed  by  this  mirror  is  13.2  mm.  in  diameter  or 
about  1.36  square  cm.  in  area.  The  energy  at  the  focus  then  amounts 
to  approximately  30  watts  per  square  cm.  A  pupil  expanded  to  say 
10  mm.  by  the  use  of  mydriatics  would  therefore  take  in  a  pencil 
equivalent  to  about  24  X  107  ergs  per  second.  Allowing  as  in  other 
cases  one-third  for  the  energy  absorbed  by  the  media  of  the  eye  as  a 
whole,  the  energy  incident  in  the  image  would  be  approximately  16  X 

107  ergs  per  second.     The  diameter  of  the  image  in  this  case  is  just 
over  2.5  mm.,  corresponding  quite  exactly  to  an  area  of  5  square  mm. 
The  energy  density  in  the  retinal  image  therefore  would  be  about  32  X 

108  ergs  per  second  per  square  cm.  and  it  was  found  in  our  experiments 
that  an  exposure  of  j  second  to  this  intensity  was  sufficient  to  produce 
a  destructive  thermic  effect  in  the  retina.     This  short  period  is  very 
striking  in  comparison  with  the  relatively  long  exposures  necessary  to 
produce  typical  eclipse  blindness  with  the  naked  eye,  although  it 
agrees  very  well  with  the  data  which  we  later  cite  regarding  energy 
burns  from  other  sources.     The  secret  of  the  relative  resisting  power 
of  the  naked  eye  is  that  usually  "in  observations  of  the  sun,  the  pupil 
is  in  extreme  miosis,  so  that  the  amount  of  energy  received  is  probably 
not  more  than  6%  of  that  computed  for  the  normal  pupil,  while  the 
extremely  small  area  of  the  solar  image  favors  rapid  dissipation  of  the 
energy  not  found  when  a  considerable  area  is  attacked,  as  in  the  case 
of  the  mirror  experiments.     The  latter  condition  we  have  often  noted 
in  thermal  experiments  of  other  sorts  with  the  big  mirror  and  lenses 
of  various  kinds.     A  concentration  of  energy  very  much  greater  than 
that  from  the  mirror,  acts  much  more  sluggishly  on  inflammable 
material  when  the  focus  is  merely  a  minute  point  instead  of  an  ap- 
preciable area.     Another  factor  that  tends  to  protect  the  human  eye 
from  the  thermic  action  of  light  sources  of  small  size,  is  the  impos- 
sibility of  perfect  fixation  for  any  length  of  time.     This  is  well  shown 
by  some  experiments  on  our  own  eyes  (see  page  732). 

The  screens  employed  in  the  work  are  noted  in  connection  with  the 
various  experiments.  Inasmuch  as  silver  reflects  very  badly  in  the 
region  near  the  extreme  ultra  violet  end  of  the  solar  spectrum  and  it 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          723 

appeared  not  desirable  to  eliminate  the  possibility  of  specific  injury 
due  to  such  rays  we  employed  in  part  of  the  experimental  work  as  a 
substitute  of  the  mirror  in  the  concentration  of  the  solar  energy  a 
quartz  lens  12  cm.  in  diameter  and  25  cm.  focal  length  mounted  on 
an  adjustable  stand  so  that  we  could  work  directly  in  its  focus. 
A  priori  the  climical  evidence  is  strongly  against  any  definite  pathologi- 
cal effects  due  to  the  ultra  violet  radiation  as  such.  Numerous  cases 
are  recorded  in  which  typical  eclipse  blindness  has  been  produced 
through  ordinary  spectacle  lenses,  through  glass  insufficiently  dark, 
and  through  opera  glasses  and  the  like,  in  all  of  which  cases  the  abiotic 
rays  are,  as  we  have  already  shown,  cut  off.  Even  very  small  thick- 
nesses of  colored  or  even  clear  glasses  are  sufficient  completely  to  ab- 
sorb these  rays,  which  moreover  are  always  cut  off  by  the  lens  so  that 
they  cannot  reach  the  retina  where  the  lesions  are  found.  This  is  in 
accordance  with  the  conclusions  reached  by  Parsons  265  in  analyzing 
the  evidence  at  hand.  Attempts  have  been  made  by  several  investi- 
gators, notably  Birch-Hirschfeld,  to  eliminate  the  infra  red  rays  also 
by  the  use  of  thick  water  cells  and  other  absorbing  media,  but  these 
attempts  so  far  as  experiments  with  solar  light  are  concerned  are  fu- 
tile, because,  as  a  glance  at  Figure  5  (page  705)  will  show,  the  greater 
portion  of  the  solar  energy  lies  entirely  within  the  visible  spectrum  with 
its  intense  maximum  in  the  blue  or  green  according  to  the  effect  of  the 
atmospheric  absorption,  so  that  for  solar  radiation  it  is  the  light  rays 
which  are  thermally  effective,  the  energy  radiation  in  the  ultra  violet 
and  infra  red  being  relatively  insignificant.  Our  experiments  show 
with  the  utmost  distinctness  that  the  effects  known  as  eclipse  blind- 
ness are  wholly  thermic,  due  to  the  intense  concentration  of  the  solar 
energy  upon  the  retina  by  the  refracting  system  of  the  eye  itself 
forming  an  image  of  destructive  energy  intensity,  the  amount  of  which 
we  have  already  computed  in  considering  the  energy  concentrated  in 
images.  It  is  only  the  briefness  of  the  casual  fixations  of  the  sun,  and 
the  great  reduction  of  the  size  of  the  pupil  in  response  to  the  intense 
illumination,  that  prevents  the  very  common  occurrence  of  such 
injuries.  In  the  observation  of  an  eclipse  the  patient  is  tempted  to 
dangerously  long  fixation  and  the  necessary  results  follow. 

With  long  fixation  the  typical  retinal  lesions  of  eclipse  blindness 
may  be  produced  by  sources  of  moderate  intensity.  For  instance  in 
our  experiment  No.  53  an  exposure  of  twelve  minutes  was  made  on 
the  eye  of  an  albino  rabbit  with  the  single  quartz  lens  system  and  the 
magnetite  arc  as  source,  through  the  5  cm.  quartz  water  cell.  Now 
from  experiments  previously  made  on  the  radiation  from  the  magnetite 


724  VERHOEFF   AND   BELL. 

arc  by  one  of  us  the  energy  entering  the  pupil  was  of  the  order  of 
magnitude  of  444,000  ergs  per  second.  Examination  of  the  retina 
showed  that  the  lesion  produced  was  practically  3  mm.  in  diameter. 
Hence  the  concentration  of  the  energy  in  the  image  allowing  the  same 
absorption  as  in  the  previous  computation  amounted  to  nearly  42  X 
106  ergs  per  second  per  square  cm.  This  is  roughly  •%$  of  the  concen- 
tration in  a  direct  solar  image  and  correspondingly  the  lesion  produced 
was  comparable  with  that  of  a  typical  case  of  eclipse  blindness.  It  is 
quite  impossible  to  get  an  accurate  idea  of  the  critical  length  of  fixa- 
tion which  appears  in  cases  of  eclipse  blindness,  since  the  observations 
producing  it  are  generally  discontinuous  and  not  noted.  This  ex- 
periment, however,  indicates,  making  due  allowance  for  the  extent 
of  the  experimental  image  and  for  the  extremely  small  size  of  the 
pupil  in  looking  at  the  sun  with  the  naked  eye,  that  the  critical  period 
for  the  development  of  eclipse  blindness  is,  with  close  fixation,  of  the 
order  of  magnitude  of  a  minute  or  less.  An  exposure  of  even  a  few 
seconds  would  be  highly  dangerous  were  it  not  for  the  extreme  miosis 
set  up  and  the  usual  wandering  of  the  image  upon  the  retina. 

Rapid  shifting  of  the  focal  image  on  the  retina  gives  the  tissue  an 
opportunity  for  cooling,  so  that  if  the  fixation  at  a  single  point  is  not 
long  enough  to  produce  destructive  effects  little  permanent  damage 
can  be  done,  although  the  scotomata  may  be  severe.  Our  experi- 
ments Nos.  100  and  101,  in  which  the  exposure  to  the  solar  heat 
through  a  blue  uviol  screen  was  intermittent,  show  this  excellently. 
In  the  first  the  exposure  was  fox  alternate  seconds  over  a  period 
aggregating  ten  minutes,  or  more  than  six  times  as  long  as  necessary 
to  produce  burning  of  the  retina  in  a  continuous  exposure.  No 
damage  was  done.  The  second  experiment,  in  which  no  water  cell 
was  used,  consisted  of  220  exposures  of  \  second  with  one  to  three 
seconds  interval  between.  In  this  case  there  was  again  no  damage 
done  although  the  exposure  was  three  and  two-thirds  times  as  long  as 
was  required  to  produce  destructive  lesions  of  the  retina  in  two  differ- 
ent cases  with  a  continuous  exposure. 

In  this  connection  one  may  note  that  the  experiment  of  Best 27  in 
fixing  the  sun  for  ten  seconds  through  a  screen  of  blue  uviol  glass  was 
a  somewhat  hazardous  one  since  this  glass  lets  through  a  very  mate- 
rial proportion  of  the  energy  from  a  high  temperature  source  like  the 
sun.  Best's  purpose  in  making  this  experiment  was  to  show  that 
ultra  violet  light  is  not  injurious  to  the  retina  of  a  normal  eye.  The 
exposure  however,  was  too  brief  for  the  result  to  be  of  importance  in 
this  regard.  It  is  not  ultra  violet  energy  which  is  to  be  feared  in  a 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         725 

case  like  this  as  we  have  already  shown,  but  the  danger  was  from  pure 
heat  radiation  of  which  10%  to  15%  was  due  to  pass  through  the 
uviol  glass.  We  produced  in  experiment  No.  97  most  destructive 
effects  from  solar  heat  passing  through  this  medium,  and  while  Best's 
experiment  of  ten  seconds  was  below  the  danger  limit  it  should  never 
be  forgotten  that  the  solar  energy  lies  well  toward  the  blue  end  of 
the  spectrum,  and  media  which  successfully  cut  out  the  red  and  infra 
red  are  of  very  little  service  in  protection  against  solar  radiation. 


THERMIC  EFFECTS  ON  THE  RETINA  FROM  SHORT  CIRCUITS. 

It  is  worth  noting  in  connection  with  eclipse  blindness  that  sources 
of  intense  energy  other  than  the  sun  may  produce  similar  results. 
For  example,  Uhthoff 373  reports  the  case  of  a  patient  exposed  to  a 
violent  short  circuit  in  which  a  fortnight  after  the  accident  grayish 
spots  due  to  alterations  in  the  pigment  epithelium  were  observable 
in  the  macula  of  the  left  eye  and  were  still  observable  six  months  later. 
This  ophthalmoscopic  appearance  is  closely  similar  to  that  many 
times  recorded  in  eclipse  blindness.  Still  later  Knapp  205  records  a 
case  of  bilateral  injury  produced  by  a  tremendously  powerful  short 
circuit  occurring  a  scant  half  meter  from  the  patient's  face.  There 
was  complete  temporary  scotoma  followed  on  the  next  day  by  some 
superficial  symptoms  indicating  photophthalmia,  and  a  week  later  by 
metamorphopsia,  while  the  vision  had  been  steadily  sub-normal. 
In  each  fundus  was  a  patch  corresponding  to  the  image  of  the  short 
circuit  flare,  in  which  serious  damage  had  been  done.  These  injured 
areas  were  still  obvious  a  year  later.  The  retinal  lesions  described, 
and  especially  the  metamorphopsia,  are  such  as  are  typical  in  the  case 
of  eclipse  blindness.  Here  the  energy  radiation  of  the  short  circuit 
was  concentrated  in  the  image  to  an  extent  sufficient  to  produce  a 
typical  thermic  lesion.  The  slightness  of  the  abiotic  radiation  re- 
ceived is  evidenced  by  the  very  brief  superficial  symptoms,  and  the 
retinal  injury,  owing  to  the  absorption  of  practically  the  whole  ultra 
violet  by  the  media  of  the  eye,  must  have  been  due  essentially  to 
the  pure  energy  radiation  of  which  the  amount,  judging  by  the  de- 
scription, was  probably  not  less  than  100  to  200  kw.  A  short  circuit 
involving  100  kw.  would  give  a  superficial  intensity  at  a  half  meter  of 
over  30,000,000  ergs  per  square  cm.,  that  is,  more  than  thirty  times 
the  intensity  of  solar  radiation.  The  area  of  the  scotoma  produced 


726  VERHOEFF  AND  BELL. 

was,  from  the  description,  in  the  neighborhood  of  1  sq.  mm.  Assum- 
ing a  pupillary  diameter  of  5  mm.  likely  to  be  found  in  working  in  a 
moderate  degree  of  light  when  surprised  by  the  short  circuit,  the 
energy  entering  the  pupil  would  be  at  least  6  X  106  ergs  per  second 
concentrated  in  the  image,  that  is  an  energy  density  amounting  to  in 
the  neighborhood  of  6  X  108  ergs  per  second  per  square  centimeter 
reckoned  without  regard  for  absorption.  Allowing  one  third  of  the 
energy  absorbed  in  the  eye  the  energy  density  in  the  image  should  be 
4  X  108  ergs  per  second  per  square  cm.  two  or  three  times,  at  least, 
greater  than  the  corresponding  energy  density  for  a  direct  observation 
of  the  sun,  very  possibly,  owing  to  the  intensity  of  the  short  circuit, 
even  several  times  greater  than  this.  It  is  little  wonder  then  that 
although  the  exposure  time  is  stated  to  be  less  than  1  second  the  results 
were  serious.  In  true  eclipse  blindness  the  length  of  fixation  is  the 
chief  factor  in  the  damage. 


THERMIC  EFFECTS  ON  THE  RETINA  FROM  LIGHTNING  FLASHES. 

A  consideration  of  these  miscellaneous  energy  effects  on  the  eye 
would  be  incomplete  without  referring  to  the  injuries  to  the  eye 
received  from  lightning.  In  such  cases  a  sharp  distinction  must  be 
drawn  between  cases  in  which  the  patient  is  actually  struck  by  light- 
ning, with  more  or  less  serious  effects,  and  those  in  which  the  patient 
is  clearly  not  struck,  but  subject  to  direct  radiation  from  a  nearby 
flash  of  lightning.  In  the  former  class  of  injuries  electrolytic  action 
and  exceedingly  severe  nervous  shock  generally  occur  and  the  final 
results  may  include  various  grave  ocular  symptoms  sometimes  ending 
in  complete  blindness  due  to  cataract  or  atrophy  of  the  optic  nerve. 
In  the  second  class  of  cases  the  effects  are  usually  limited  to  severe 
scotomata  which  may  impair  vision  for  some  hours  or  days  but  as  a 
rule  there  are  no  lesions  visible  either  superficially  or  with  the  ophthal- 
moscope, and  no  permanent  damage  is  done.  This  immunity  is 
chiefly  due  to  the  usually  considerable  distance  between  the  actual 
lightning  bolt  and  the  observer,  since  the  amount  of  energy  actually 
involved  in  a  lightning  discharge  of  the  first  order  of  magnitude  may 
be  enormously  great.  Sir  Oliver  Lodge  estimates  it  as  high  as  1020 
ergs.  There  are  a  few  instances,  however,  in  which  the  energy  re- 
ceived at  the  eye  has  been  great  enough  to  produce  typical  lesions 
both  from  abiotic  action  and  probably  also  from  purely  thermal 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          727 

effects.  Silex337,  Vossius407,  Rivers276,  Dunbar  Roy302  and  Le 
Roux  et  Renaud  225  have  all  noted  superficial  injuries  of  the  cornea 
and  the  last  named,  as  also  Oliver  26°  have  noted  symptoms  of  chorio 
retinitis,  which  seem  to  indicate  lesions  due  to  thermic  effects,  in  the 
latter  case  invoking  the  metamorphopsia  frequently  associated  with 
eclipse  blindness.  The  case  of  Le  Roux  et  Renaud  was  a  specially 
notable  one  in  which  the  patient,  on  guard  duty  at  night,  was  exposed 
to  a  very  powerful  flash.  It  was  immediately  followed  by  violent 
erythropsia  which  lasted  for  some  two  hours.  The  Gendarme  re- 
mained at  his  post  and  went  home  and  to  bed  about  three  hours  later. 
The  next  morning  he  woke  with  acute  headache,  with  substantial 
blindness  in  the  left  eye  followed  a  few  hours  later  by  loss  of  sight  in 
the  right  eye.  There  was  double  acute  conjunctivitis  with  swelling 
and  reddening  of  the  lids  and  conjunctiva  and  marked  chemosis.  A 
little  later  there  was  diffuse  interstitial  keratitis,  a  change  in  the  color 
of  the  iris  from  blue  to  greenish  and  a  grayish  haze  on  the  lens  front 
visible  in  a  bright  light.  These  affections  of  the  anterior  eye  cleared 
later  and  when  the  ophthalmoscope  could  be  used  there  was  marked 
haze  in  the  vitreous,  which  cleared  very  slowly  and  not  completely 
even  after  three  years.  This  was  believed  by  Le  Roux  et  Renaud  to 
be  associated  with  chorio  retinitis  and  was  certainly  secondary  to  the 
original  lesions. 

It  is  very  difficult  to  make  anything  like  an  exact  computation  of 
the  energy  which  produced  these  results,  since  not  only  is  the  total 
amount  of  energy  in  a  lightning  flash  extremely  variable  and  known 
only  to  a  rough  approximation,  but  the  duration  of  the  flash  is  also 
variable  and  uncertain.  Thus  much  is  clear,  however,  that  the  very 
heavy  discharges,  in  which  the  length  of  flash  is  some  hundreds  or 
thousands  of  meters  and  the  quantity  of  electricity  discharged  very 
large,  are  also  the  relatively  slow  flashes,  since  the  equivalent  con- 
denser capacity  is  very  large.  The  estimates  of  frequency  rising  to 
millions  per  second  can  have  no  place  here,  since  obviously  the  velo- 
city of  free  waves  being  only  300,000  km.  per  second,  a  flash  of  one 
or  several  km.  in  length  cannot  have  a  very  high  oscillation  frequency 
even  supposing  it  permits  oscillations  at  all.  Attempts  to  measure 
the  frequency  of  the  discharge  have  often  led  to  results  of  less  than 
.001  of  a  second  and  it  is  altogether  probable  that  in  these  long  flashes 
there  is  no  oscillation  at  all  on  account  of  the  resistance  effects.  Start- 
ing from  the  estimate  of  Sir  Oliver  Lodge  of  1020  ergs  per  second  and 
assuming  an  effective  time  of  discharge  .0001  of  a  second,  and  that  of 
the  total  flash  not  over  .1  is  within  the  effective  range  of  reaching  the 


728  VERHOEFF  AND   BELL. 

eye,  the  energy  in  the  discharge  may  be  reckoned  as  one  or  perhaps 
several  thousand  times  that  of  the  short  circuit  discussed  in  connec- 
tion with  Knapp's  case.  With  a  nearby  discharge  occurring  say 
within  10  or  20  meters,  the  quantity  of  energy  received  by  the  eye 
would  be  amply  great  to  account  for  even  severer  results  than  those 
noted  by  Knapp  (loc.  cit.). 

Working  back  from  our  experiments  with  the  bare  magnetite  lamp 
carrying  about  500  watts  in  the  arc,  it  again  appears  that  the  quantity 
of  energy  assumed  by  Sir  Oliver  Lodge  is  more  than  sufficient  to  ac- 
count for  the  results  of  a  nearby  discharge.  It  therefore  must  be 
admitted  that  the  direct  action  of  lightning  in  producing  both  abiotic 
and  thermic  lesions  in  the  eye  as  in  the  cases  of  Le  Roux  et  Renaud 
and  of  Oliver  is  well  within  the  bounds  of  possibility  although  requiring 
very  unusual  proximity  to  a  powerful  discharge  which  may  well  have 
been  the  case  in  these  instances.  The  extreme  rarity  of  such  clinical 
conditions  is  perhaps  ascribable  to  the  few  instances  in  which  there  is 
close  proximity  to  the  stroke  combined  with  free  exposure  of  the  eyes 
without  the  patient  being  actually  involved  in  the  shock.  One  must 
consider  therefore  that  lesions  produced  directly  by  the  radiating 
energy  of  a  lightning  discharge  are  extremely  unusual  and  unlikely 
to  occur,  although  well  within  the  range  of  possibility,  as  the  cases 
here  referred  to  show. 


POSSIBLE  SPECIFIC  ACTION  OF  INFRA  RED  RADIATION. 

As  we  have  already  stated,  there  was  no  segregation  of  various 
radiations  in  our  experiments  on  thermic  effects  except  in  so  far  as 
abiotic  radiations  were  cut  off  by  certain  screens.  So  far  as  all  indi- 
cations go  the  effect  of  all  other  radiation  than  the  abiotic  is  chiefly 
chargeable  to  thermic  energy  without  respect  to  wave  length.  As 
already  explained  different  sources  present  totally  different  distribu- 
tions of  energy  with  respect  to  wave  length,  the  lower  the  temperature 
the  greater  being  the  proportion  of  the  so-called  infra-red  rays.  In 
the  case  of  the  quartz  mercury  arc  and  the  magnetite  arc  with  which 
we  chiefly  worked,  the  spectra  are  essentially  discontinuous  and  hence 
do  not  obey  Planck's  law,  so  that  there  is  no  definite  relation  between 
the  temperature  and  the  wave  length  of  maximum  radiation. 

The  total  energy  spectrum  of  each  of  these  sources,  however,  is 
exceedingly  complex.  Of  the  total  energy  spent  in  the  arc  a  certain 
proportion  goes  to  maintain  the  characteristic  linear  spectra,  a  cer- 


EFFECTS    OF    RADIANT    ENERGY   ON   THE   EYE.  729 

tain  other  portion  goes  to  heating  the  electrode  or  containing  tube  and 
the  surrounding  mechanism.  While  therefore  the  spectrum  which 
can  be  seen  or  photographed  is  linear,  there  is  superimposed  upon  it 
the  continuous  spectrum  of  the  radiating  solid  at  rather  low  tempera- 
ture and  of  relatively  large  extent,  since  the  radiation  is  not  only  from 
the  arc  or  its  containing  tube  but  from  the  immediately  heated  sur- 
roundings. Much  of  the  loss  of  efficiency  in  both  sources  referred  to 
comes  from  this  secondary  heat  radiation.  This  is  particularly  the 
case  in  the  quartz  mercury  arc  of  which  the  actual  light-giving  effi- 
ciency is  very  high,  much  higher  than  is  indicated  even  by  its  really 
small  specific  consumption  per  c.  p. 

The  existence  of  this  secondary  radiation  which  is  mainly  of  very 
long  wave  length,  make  comparisons  between  such  sources  and  the 
ordinary  radiating  solids  very  difficult.  The  following  table  gives 
for  the  magnetite  arc  the  transmission  with  respect  to  the  total  energy 
of  the  most  important  of  the  various  media  which  we  employed,  as 
determined  by  a  Rubens  thermopile. 


ABSORPTION  OF  CERTAIN  SCREENS. 

Source  Magnetite  Arc. 

Percentage 
Filter  of  Transmission 

2  quartz  plates  each  3  mm.  thick  53 

Same  +  5  cm.  distilled  water  33 

Water  cell  and  Dense  Flint  NB  1.69  (335  MM)  26 

"  "  "  Medium  Flint  ND  1.62  (315  MM)  28 

"  «  Light  Flint  ND  1.57  (305  MM)  27 

"        "      "     Crown  ND  1.51  (295  MM)  28 

Dense  Flint  ND  1.69  alone  40 

Medium  Flint  ND  1.63       "  45 

Light  Flint  ND  1.57      "  40 

Crown  ND  1.51       "  43 

It  will  be  observed  that  the  actual  transmission  of  the  empty  quartz 
cell  consisting  of  two  3  mm.  polished  plates  was  only  53%  of  the  total 
energy.  Of  the  47%  lost,  roughly  15%  should  be  in  the  reflections 
from  the  four  surfaces  of  the  two  3  mm.  polished  plates.  The  re- 
mainder, that  is  more  than  a  third  of  the  total  energy,  is  mainly 


730  VERHOEFF  AND  BELL. 

from  the  cut-off  of  secondary  radiation  of  relatively  very  long  wave 
length,  4  to  5  n  and  more,  received  from  radiating  surfaces  at  and  below 
red  heat.  The  addition  of  5  cm.  of  distilled  water  in  filling  the  cell 
reduced  the  transmitted  radiation  to  33%,  which  represents  the  radia- 
tion between  the  former  limit  and  approximately  1  ju.  There  is  every 
reason  to  believe  that  most  of  this  energy  is  from  the  hot  body  radia- 
tion rather  than  from  the  line  spectrum  of  the  arc  itself,  for  in  so  far 
as  known  metallic  spectra  are  not  rich  in  intense  infra-red  lines. 
Screen  No.  1  then,  cuts  off  22%  of  the  energy  between  1  ;u  and  the 
extreme  ultra  violet.  Screen  No.  2,  medium  optical  flint,  is  relatively 
transparent,  almost  as  transparent  as  the  light  crown  screen  No.  7, 
while  the  light  flint  screen  No.  4  cuts  off  more  energy  than  either  of 
these.  Used  without  the  water  cell  all  the  four  screens  mentioned 
cut  off  between  50  and  60  %  of  the  total  energy  due  to  the  large 
absorption  of  glass  in  the  extreme  infra  red  corresponding  to  the 
secondary  hot-body  radiation  of  the  source. 

This  secondary  radiation  being  from  a  very  diffused  source  cannot 
have  a  conspicuous  effect  in  those  experiments  in  which  the  light 
was  concentrated  through  lenses  although  it  comes  into  play  in  the 
free  radiation  from  the  arc.  It  is  quite  certain,  for  instance,  that  in 
the  bactericidal  experiments  with  the  mercury  arc  which  one  of  us 
has  recorded,  in  which  trouble  was  experienced  from  heating  of  the 
water  in  which  the  bacteria  were  suspended,  this  heating  was  mainly 
from  the  large  secondary  radiation  which  is  readily  stopped  by  water 
rather  than  from  the  characteristic  radiation  of  the  mercury  vapor. 

The  data  heretofore  given  by  one  of  us  on  the  proportion  of  ultra 
violet  energy  in  the  quartz  mercury  lamp  and  the  magnetite  arc  may 
be  regarded  as  substantially  correct  for  the  metallic  spectra  as  such, 
the  quartz  water  cell  of  1  cm.  thickness  employed  in  these  experiments 
cutting  off  the  secondary  radiations  rather  completely  without  inter- 
fering materially  with  the  energy  of  the  line  spectrum.  In  our 
experiments  involving  total  thermic  effects  necessary  corrections  for 
the  conditions  of  the  experiment  can  be  made  by  reference  to  the 
foregoing  table. 

As  regards  the  thermic  action  of  radiation  on  the  eye,  there  is  no 
reason  to  suspect  any  specific  effects  with  respect  to  wave  length. 
So  far  as  the  action  is  not  definitely  abiotic  or  concerned  with  the 
stimulation  of  the  light  perceiving  functions  of  the  retina  it  seems 
to  be  purely  a  question  of  energy  as  in  any  other  case  of  heating. 
The  more  violent  phenomena  produced  by  heating  are  considered  in 
our  discussion  of  eclipse  blindness  and  allied  phenomena  (page  720). 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         731 

The  possible  effects  on  the  lens  of  heat  radiation  persisting  over  a  very 
long  period  we  have  considered  in  discussing  glass  blowers  cataract 
(page  734).  Thermic  effects  on  the  cornea  we  have  shown  to  be 
obtainable  only  under  extreme  experimental  conditions  (page  692). 
The  media  of  the  eyes  generally,  as  we  have  already  shown,  are  of 
substantially  the  same  absorbing  character  as  water  so  far  as  concerns 
visible  and  infra  red  rays  and  therefore  take  up  chiefly  radiant  energy 
of  long  wave  length  such  as  is  prominent  in  radiation  received  from 
low  temperature  sources  like  hot  metals  or  molten  glass.  The  pig- 
mented  iris  and  the  pigment  epithelium  of  the  fundus  are  exceptions 
in  that  they  absorb  quite  completely  radiant  energy  irrespective  of 
wave  length.  There  is,  therefore,  a  tendency  to  produce  localized 
thermic  effects  in  both  these  structures,  as  we  have  shown  in  various 
of  our  experiments.  The  lesions  occurring  under  these  circumstances 
have  already  been  described.  In  case  of  the  iris,  the  heat  effects  may 
proceed  all  the  way  from  moderate  irritation  to  serious  permanent 
injury  (see  page  696).  This  phase  of  the  matter  was  recently  inves- 
tigated by  Reichen293.  This  observer  studied  the  effects  of  con- 
centration of  infra  red  radiation  on  the  eye  by  cutting  off  the  visible 
and  ultra  violet  spectrum  by  a  filter  of  iodine  in  bisulphide  of  carbon, 
and  absorbing  the  extreme  infra  red  by  a  water  filter.  In  this  way 
the  rays  with  which  he  was  concerned  were  substantially  those  be- 
tween 800  and  1200  nn.  Using  as  source  the  electric  arc  between 
carbon  electrodes,  by  means  of  a  rock  salt  lens  he  concentrated  the 
filtered  energy  upon  the  eyes  of  rabbits  for  periods  from  1  to  33  min- 
utes. The  only  effect  noted  was  contraction  of  the  pupil  lasting  some 
hours  and  generally  slight,  evidently  depending  on  the  direct  heat 
effect  through  the  filters  used,  since  the  visible  rays  were  practically 
excluded  from  the  retina.  Such  pupillary  contraction  is  reasonably 
to  be  expected  after  moderate  irritation  of  the  iris,  such  as  would  be 
furnished  by  this  heat  stimulus  and  may  occur  as  some  of  our  experi- 
ments show,  in  the  absence  of  any  recognizable  histological  changes. 
Violent  and  persistent  effects  were  hardly  to  be  expected  inasmuch  as 
the  source  used  is  not  rich  in  rays  transmissible  through  Reichen's 
filters.  Most  of  the  energy  from  a  carbon  arc  is  intercepted  by  a  water 
filter  and  a  good  deal  of  the  remaining  energy  by  the  iodine  in  carbon 
bisulphides.  This  selective  action  is  well  shown  in  one  of  Reichen's 
experiments  in  which  the  water  screen,  which  was  quite  close  to  the 
arc,  was  boiling  violently  after  1\  minutes  exposure.  Reichen's  experi- 
ments, therefore,  merely  show  a  mild  irritation  not  in  the  least  peculiar 
to  the  region  of  the  spectrum  employed.  It  would  seem  quite  im- 


732  VERHOEFF   AND   BELL. 

possible  to  obtain  even  this  effect  except  through  strong  focussing  of 
the  light  upon  the  eye,  a  condition  which  is  not  found  in  the  use  of 
ordinary  illuminants  for  any  purpose.  So  far  then  as  infra  red 
radiation  is  concerned  the  eye  is  not  subject  to  any  special  dangers, 
and  the  concentration  of  heat  upon  it  in  any  way  would  inevitably  set 
up  a  danger  signal  of  painful  sensation  long  before  any  definite  heat 
effects  could  be  obtained. 

In  fact  it  is  easily  demonstrable  that  the  full  radiation  that  can 
under  practical  conditions  be  received  from  the  most  powerful  illumi- 
nants is  incapable  of  producing  on  the  retina  any  lesions  due  to 
thermic  action  such  as  may  be  found  in  eclipse  blindness.  In  our 
Experiment  53,  already  referred  to,  changes  in  the  pigment  epithelium 
and  a  definite  burnt  area  were  produced.  The  diameter  of  the  area 
in  which  histological  changes  were  clear  was  3  mm.  shading  off  toward 
the  edges  and  having  a  central  area  about  1  mm.  in  diameter,  in  which 
the  damage  was  serious  and  comparable  with  that  in  eclipse  blindness. 
We  have  found  that  in  this  case  the  concentration  of  the  energy  in 
the  image  amounted  to  very  nearly  4.2  X  106  ergs  per  second  per 
square  cm.,  roughly  ^  of  that  found  in  the  solar  image  formed  directly 
through  a  3  mm.  pupil.  The  exposure  to  this  intensity  lasted  12 
minutes.  Here  then  is  a  definite  case  in  which  the  result  was  positive. 
Negative  results,  however,  of  which  a  few  were  obtained  in  our  experi- 
ments, are  unsatisfactory  since  they  do  not  take  account  of  the  wan- 
dering of  the  image,  or  of  imperfect  fixation  which  as  we  have  shown 
would  be  likely  to  avert  injury  as  in  the  typical  case  of  intermitted 
exposure  to  heat. 

Our  large  magnetite  arc  gives  at  a  distance  of  2  meters  a  total 
radiation  of  about  2500  ergs  per  second  per  square  cm.  At  this  dis- 
tance from  the  arc  we  find  the  pupil  of  the  human  eye  is  narrowed  to  a 
scant  2  mm.  and  this  area  would  intercept  about  75  ergs  per  second 
of  the  total  amount  stated,  allowing  3  absorption  as  heretofore. 
This  means  that  the  energy  concentrated  on  the  retina  would  be  about 
50  ergs  per  second.  To  compute  the  energy  density  requires  a  knowl- 
edge of  the  size  of  the  image  including  the  element  of  imperfect 
fixation.  We  have  found  from  personal  experiments  that  on  fixing 
at  2  meters  the  magnetite  arc  for  a  few  seconds  and  measuring  the 
size  of  the  scotoma  produced  by  viewing  at  the  same  distance  a  card 
ruled  to  centimeters,  that  even  for  this  short  fixation  period  the  area 
of  the  scotoma  is  nearly  four  times  that  of  the  geometrical  image  of 
the  source.  On  fixation  of  6  minutes  the  scotoma  rises  to  twenty-five 
times  the  size  of  the  geometrical  image.  This  latter  has  an  area  of 


EFFECTS   OF   RADIANT   ENERGY  ON  THE   EYE.  733 

about  0.01  square  mm.  as  determined  from  photographic  data,  so 
that  for  a  long  fixation  the  energy  received  would  be  distributed  over 
practically  j  square  mm.  of  area.  The  density  in  the  image  as  actu- 
ally obtained  in  a  long  fixation  would  amount  to  about  20,000  ergs 
per  second  per  square  cm.,  only  about  ^  Par^  °f  the  energy  density 
which  produced  the  positive  result  in  experiment  No.  53.  This 
difference  is  still  further  enhanced  practically  by  considerable  differ- 
ence in  the  size  of  the  image  areas,  the  smaller  one  being  relatively  less 
effective  than  the  large  on  account  of  the  more  rapid  dissipation  of 
heat.  It  is  therefore  evident  that  an  exposure  of  even  12  minutes 
with  close  fixation  to  a  source  as  powerful  as  this  arc,  a  thing  which  no 
rational  human  being  would  be  likely  to  undertake,  still  involves  only 
a  small  fraction  of  the  minimum  energy  known  to  produce  definite 
lesions. 

Further  evidence  of  the  harmlessness  of  such  exposures  even  to 
very  powerful  artificial  illuminants  may  be  derived  from  noting  that 
the  heat  concentration  in  this  case,  that  is  20,000  ergs  per  second  per 
square  cm.  is  less  than  5^5,  of  that  received  by  direct  fixation  of  the 
sun  with  the  same  pupillary  aperture  (see  page  719).  Now  it  is 
well  known  that  one  can  fix  the  sun  for  a  very  few  seconds  without 
danger  of  anything  more  than  a  temporary  scotoma.  From  this  we 
may  conclude  that  the  arc  here  considered  may  be  fixed,  as  well  as  it  is 
possible  to  secure  fixation,  for  a  considerable  period  without  running 
danger  of  a  permanent  scotoma. 

In  order  to  demonstrate  beyond  any  possibility  of  doubt  that  the 
retina  cannot  be  injured  by  exposure  of  the  eye  to  a  source  such  as 
the  magnetite  arc,  one  of  us  has  actually  fixed  his  eye  upon  this  arc 
at  a  distance  of  two  meters  for  6  minutes  on  two  occasions.  The 
macula  itself  was  not  fixed  upon  the  arc  but  upon  an  object  of  the 
same  size  placed  2.6°,  to  one  side  of  it.  In  this  way  more  perfect 
fixation  of  the  image  of  the  arc  on  the  retina  was  ensured  than  if  the 
arc  had  been  looked  at  directly.  The  results  were  only  of  a  tempo- 
rary character.  There  was  considerable  xanthopsia  lasting  about 
3  minutes.  The  scotoma  had  disappeared  after  each  observation  in 
less  than  ten  minutes  and  could  only  be  detected  for  a  few  hours  by 
careful  dark  adaptation  of  the  eye.  The  following  day  no  traces  of  it 
were  determined.  It  is  therefore  clear  from  actual  experiment  as  well 
as  from  general  principles  that  even  the  extremely  powerful  arc  which 
we  have  here  used  is  from  the  standpoint  of  injury  to  the  retina  entirely 
harmless  under  any  circumstances  conceivable  in  practical  use.  Some 
large  carbon  arcs  may  yield  even  two  or  six  times  the  total  heat  energy 


734  VERHOEFF  AND  BELL. 

of  the  magnetite  arc  here  in  question  while  yet  remaining  within 
perfectly  safe  limits  from  any  practical  standpoint.  No  actual  arti- 
ficial illuminant  can  fairly  be  considered  dangerous  from  the  standpoint 
of  thermic  action  on  the  retina.  It  will  be  observed  that  since  no 
screens  were  used,  these  experiments  also  afford  evidence  of  the  harm- 
lessness  of  abiotic  radiations  to  the  retina. 


GLASSBLOWERS'  CATARACT. 

The  fact  that  glassblowers  are  subject  to  a  special  form  of  cataract 
has  naturally  raised  the  question  whether  or  not  the  latter  is  due 
to  radiant  energy  and  if  so,  whether  to  abiotic  or  thermic  action. 
Meyhofer  245  examined  506  glassmakers  and  found  11.6%  affected  with 
cataract.  The  cataract  almost  always  appears  first  in  the  left  eye 
which  is  the  more  exposed  to  the  light.  When  it  appears  first  in  the 
right  eye  it  has  been  found  that  the  glassblower  has  been  in  the 
habit  of  turning  this  eye  towards  the  oven  (Stein  349) .  The  glassblow- 
ers show  also  a  peculiar  rusty  brown  spot  on  each  cheek,  more  marked 
on  the  left.  The  length  of  time  necessary  for  the  development  of  the 
cataract  has  not  been  exactly  ascertained,  but  it  is  evidently  several 
years.  The  cataract  usually  begins  before  the  age  of  40.  In  Mey- 
hofer's  series  the  youngest  blower  was  aged  15  years  and  the  youngest 
affected  with  cataract  17  years.  Of  59  cases  of  cataract,  42  were  under 
the  age  of  40.  In  the  latter  cases,  both  eyes  were  affected  in  16,  the 
left  eye  alone  in  19,  and  the  right  eye  alone  in  7.  The  glassblowers 
are  thin  and  delicate,  and  are  subject  to  asthma  and  pulmonary  tuber- 
culosis. Almost  all  of  them  have  emphysema  of  the  parotid  gland. 
During  their  working  hours  they  perspire  excessively  and  in  conse- 
quence drink  enormous  quantities  of  fluids,  including  beer,  coffee, 
wine,  and  lemonade. 

The  cataract  begins  as  a  rosette  like  or  diffuse  opacity  in  the  cortex 
at  the  posterior  pole  of  the  lens,  the  remainder  of  the  lens  for  a  long 
time  remaining  clear.  Later,  striae  similar  to  those  of  senile  cataract 
may  appear.  At  operation  the  nucleus  is  found  larger  than  that  of 
other  individuals  of  the  same  age  (Stein349),  and  the  capsule  more 
fragile  (Cramer81).  Parsons265  states  that  in  only  one-fifth  of  the 
cases  does  the  cataract  differ  in  appearance  from  a  senile  cataract, 
but  this  probably  applies  to  the  late  stages. 

Hirschberg 192  states  that  for  over  100  years  it  has  been  recognized 
by  various  observers  that  individuals  exposed  to  intense  heat  and  light 


EFFECTS   OF    RADIANT    ENERGY   ON   THE    EYE.  735 

are  especially  liable  to  cataract.  Peters 272  suggested  that  the  cata- 
ract was  due  to  the  venous  stasis  in  the  vortex  veins  associated  with 
the  forced  expiration,  analogous  to  the  cataract  produced  experi- 
mentally by  tying  off  the  vortex  veins.  Leber  222  advanced  the  view 
that  it  was  due  to  concentration  of  the  aqueous  resulting  from  evapo- 
ration from  the  cornea  and  the  loss  of  water  from  excessive  perspira- 
tion. Parsons 265  suggested  that  the  cataract  results  from  altered 
nutrition  due  to  overheating  of  the  ciliary  body.  Cramer  81,  Stein  349, 
and  others  believe  that  it  is  due  to  ultra  violet  light  (chemical  action), 
while  Vogt 3"  regards  the  infra  red  rays  as  chiefly  responsible. 

The  great  frequency  with  which  glassblowers'  cataract  occurs,  its 
relatively  uniform  type,  and  the  fact  above  all,  that  it  occurs  first  in 
the  more  exposed  eye,  show  clearly  enough  that  it  is  chiefly  due  to  the 
action  of  radiant  energy  on  the  eye  itself.  This  is  supported  also  by 
the  fact  that  the  cheek  shows  a  more  marked  area  of  discoloration  on 
the  side  of  the  first  affected  eye.  The  further  questions  whether  the 
cataract  is  due  to  the  direct  action  of  the  light  upon  the  lens,  or  upon 
the  eye  as  a  whole,  and  whether  it  is  due  to  abiotic  or  thermic  action, 
are  not  quite  so  easily  answered. 

The  character  of  the  radiation  from  molten  glass  is  well  known.  It 
is  that  from  a  homogeneous  body  of  relatively  low  temperature,  1200° 
to  1400°  C.  It  is  certain  that  the  spectrum  of  a  non  gaseous  body 
at  this  temperature  does  not  include  any  of  the  so-called  abiotic  radia- 
tion since  the  extreme  limit  of  the  spectrum  of  molten  glass  found  by 
any  investigator  is  320  /j,fj,  and  estimates  range  from  that  to  334  /i/i. 
We  have  already  shown  that  the  abiotic  action  cannot  be  traced 
beyond  305  ju/x  and  there  is  not  the  slightest  indication  from  our 
researches  or  any  predecessors  that  there  is  reason  to  suspect  an 
extension  of  such  activity  to  waves  longer  than  320  ju/x.  Even  if 
there  were,  such  rays  would  be  stopped  at  the  front  of  the  lens  by  its 
absorption  and  hence  would  be  unable  to  affect  the  posterior  cortex. 
Moreover  the  radiation  of  a  body  at  such  temperature  is  relatively 
very  weak  all  through  the  ultra  violet,  the  maximum,  according  to 
Planck's  law,  for  a  body  at  1300°  C.  lying  far  in  the  infra  red 
while  the  energy  in  the  whole  visible  and  ultra  violet  part  of  the 
spectrum  is  less  than  1%  of  the  total.  Hence  to  ascribe  injurious 
effects  to  the  visible  or  ultra  violet  radiation  without  eliminating 
once  and  for  all  the  99%  of  infra  red  radiation  is  to  lose  all  sense 
of  proportion  between  cause  and  effect.  To  follow  up  the  theory 
of  the  matter  a  little  further  we  have  shown  that  the  specific 
abiotic  action  is  clearly  to  be  eliminated.  Of  the  rays  which  are 


736  VERHOEFF   AND    BEI^L. 

absorbed  by  the  lens,  reaching  from  300  /x/x  to  about  400  ^u,  the  chief 
absorption  is,  following  the  general  theory  which  we  have  already 
explained,  at  the  front  surface,  hence  if  by  any  stretch  of  the  imagina- 
tion glassblowers'  cataract  could  be  assumed  to  be  due  to  an  indefi- 
nitely long  application  of  such  rays  it  should  occur  at  the  anterior  and 
not  at  the  posterior  cortex.  To  rays  in  the  ordinary  visible  spectrum 
the  lens  is  notoriously  transparent  and  in  default  of  absorption  of 
energy  there  is  no  reason  to  expect  any  specific  effects  from  it.  We 
have  been  able  by  the  use  of  sources  of  extreme  power  greatly  concen- 
trated, as  our  experiments  show,  to  obtain  specific  action  of  the  ultra 
violet  rays  only  to  a  microscopic  depth,  20  /x,  so  that  the  experimental 
evidence  lies  squarely  against  any  lesions  directly  producible  by  such 
sources  in  the  posterior  cortex,  particularly  in  the  absence  of  any  effects 
in  the  anterior  cortex. 

This  reasoning  also  holds  for  the  time  integrals  of  any  effect  of  such 
rays  over  periods  however  long,  for  whatever  the  aggregate  effect 
might  be  it  would  always  remain  much  greater  at  the  anterior  than  at 
the  posterior  part  of  the  lens  substance.  The  absorption  of  the  media 
of  the  eye  for  various  wave  lengths  and  especially  those  predominant 
in  sources  of  the  temperature  considered  has  been  investigated  by 
Aschkinass 5  who  has  shown  that  the  characteristic  absorption  of  the 
long  waves  is  essentially  that  of  water.  An  analysis  of  Aschkinass' 
results  by  Luckiesh  23°  shows  that  for  sources  of  moderate  temperature 
the  resulting  absorption  is  chiefly  in  the  cornea  and  aqueous,  that  is  in 
the  outer  layers  of  the  absorbing  media.  For  a  source  of  the  tempera- 
ture of  a  glass  furnace,  between  80  and  90%  of  the  energy  will  be 
absorbed  by  the  cornea  alone,  and  the  amount  stopped  in  the  lens 
from  all  causes  would  not  be  over  3  or  4%,  but  this  small  fraction  of 
the  total  is  still  absolutely  a  considerable  quantity  and  is  somewhat 
concentrated  in  the  lens  since  not  less  than  three-fourths  of  the  total 
refraction  of  the  eye  is  due  to  the  cornea.  There  is  therefore  a  slight 
tendency  to  concentrate  energy  toward  the  rear  of  the  lens.  Such 
concentration  must  be  small,  however,  owing  to  the  contracted  pupil 
and  the  resulting  narrow  angle  of  the  pencil  of  rays  entering  the  lens. 
It  is  doubtful  whether  the  actual  concentration  would  reach  more  than 
a  few  per  cent  and  the  effect  of  this  would  be  more  than  offset  by  the 
greater  absorption  in  the  anterior  cortex. 

As  regards  the  distribution  of  temperature  in  the  eye  resulting  from 
the  intense  radiation  most  of  the  absorption  takes  place  as  stated,  in 
the  cornea,  and  a  greater  proportion  in  the  aqueous  than  in  the  lens. 
The  front  of  the  cornea  is  of  course  rapidly  cooled  by  convection  and 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         737 

the  fluid  of  the  anterior  chamber  also  gets  some  facility  at  cooling  by 
convection  currents.  The  iris  which  strongly  absorbs  most  of  the 
energy  which  falls  upon  it  especially  if  strongly  colored,  to  a  certain 
extent  screens  the  front  surface  of  the  lens  behind  it  especially  since 
the  circulatory  system  in  the  iris  tends  to  prevent  its  temperature 
rising  materially  unless  the  access  of  energy  is  above  the  rate  at  which 
circulation  can  take  care  of  it.  At  the  rear  of  the  lens  the  vitreous 
with  its  fibrillated  structure  effectively  prevents,  like  all  such  sub- 
stances, the  existence  of  convection  currents.  Just  what  the  net 
effect  of  the  structure  is  upon  the  steady  distribution  of  temperature 
when  the  eye  is  exposed  to  radiation  cannot  be  quantitatively  de- 
termined, and  while  undoubtedly  the  heat  reaching  the  rear  of  the 
lens  from  the  energy  transmitted  to  that  point,  or  received  from  that 
taken  up  by  absorption  in  the  anterior  part  of  the  eye,  cannot  readily 
escape  and  hence  tends  toward  concentration  it  seems  somewhat 
doubtful  whether  this  cause  alone  could  determine  the  starting  of 
cataract  at  the  posterior  cortex.  We  are  inclined  to  attach  more 
importance  to  the  suggestions  of  Leber  m  that  the  effect  is  a  secondary 
one  due  to  the  loss  of  water  in  the  drain  produced  by  the  heat  on  the 
front  of  the  eye  and  elsewhere,  and  especially  to  that  of  Parsons  265 
that  malnutrition  due  to  interference  with  the  functions  of  the  ciliary 
body  by  the  heat  may  be  chargeably  with  the  malady.  We  are  the 
more  inclined  to  this  opinion  since  the  intense  radiation  acts  through 
the  sclera  as  well  as  through  the  cornea,  thus  affecting  the  whole 
structure.  It  is  also  a  well  known  clinical  fact  that  diseases  of  the 
fundus  produce  at  times  cataractous  changes  in  the  posterior  cortex 
that  are  held  to  be  due  to  impaired  nutrition  of  the  lens.  The  develop- 
ment of  glass  blowers'  cataract  is  so  slow  that  it  is  quite  hopeless  to 
reach  its  cause  experimentally,  but  from  the  facts  here  stated  we 
incline  to  the  opinion  that  these  secondary  effects  of  radiation  are 
more  important  in  producing  it  than  the  specific  action  of  radiation  in 
producing  localized  effect  at  the  posterior  cortex.  In  any  case  it  is 
perfectly  clear  that  abiotic  radiations  are  not  concerned,  and  have 
nothing  to  do  with  the  matter. 


APPLICATIONS  TO  COMMERCIAL  ILLUMINANTS. 

In  considering  any  possible  deleterious  effects  of  radiation  upon 
the  eye  there  are  certain  pathological  effects  which  can  be  at  once 
eliminated,  at  least  from  any  consideration  of  commercial  illuminants. 


738  VERHOEFF   AND    BELL. 

First,  by  the  experiments  which  have  been  heretofore  described  we 
have  made  it  clear  that  there  can  be  no  injury  done  to  the  retina  by 
ultra  violet  light  as  such,  even  the  most  severe  exposures  failing 
completely  to  produce  any  effect  whatever.  Second,  all  thermic 
effects  of  energy  from  any  source  on  the  external  eye  are  at  once 
ruled  out  of  consideration  by  the  immediate  discomfort  produced  by 
excessive  heat.  No  person  would  tolerate  extreme  heat  radiation  on 
the  external  eye  for  a  period  long  enough  to  produce  the  slightest 
damage.  There  remain  therefore  to  be  considered  thermic  effects 
within  the  eye,  and  specially  those  due  to  the  focussing  of  intense 
radiation  upon  the  retina  as  in  eclipse  blindness;  over  stimulation  of 
the  physiological  processes  in  the  retina,  that  is  pathological  effects 
due  to  light  as  such  in  its  action  on  the  retinal  structure,  and  finally 
those  abiotic  effects  of  the  extreme  ultra  violet  rays  on  the  external 
eye  properly  known  as  photophthalmia.  It  has  been  our  purpose  to 
ascertain  the  practical  risks  incurred  in  the  use  of  artificial  illuminants 
and  the  precautions  required  to  avoid  danger.  To  this  end  have  we 
sought  especially  the  quantitative  relations  in  the  action  of  radiant 
energy  upon  the  eye.  We  have,  therefore,  experimented  with  the 
most  powerful  sources  used  for  practical  lighting  under  conditions  of 
intensity  immensely  greater  than  occur  in  their  every  day  use.  We 
have  shown  (page  728)  that  as  regards  the  general  thermic  effects  of 
energy  upon  the  eye  there  is  no  chance  of  damage  to  the  retina  or  to 
the  media  of  the  eye  under  any  practical  conditions  of  use.  With 
respect  to  damage  to  the  retina  in  particular  we  have  been  unable  to 
produce  it  except  by  exposures  and  intensities  enormously  greater 
than  could  possibly  be  reached  in  the  use  of  artificial  sources  of  light. 
We  have  used  beside  the  quartz  mercury  arc  which  is  not  particularly 
strong  in  general  radiation,  a  750  watt  magnetite  arc  which  takes  the 
greatest  amount  of  energy  of  any  arc  light  ordinarily  used  for  illumi- 
nating purposes  and  the  750  watt  nitrogen  lamp  which  gives  more 
ultra  violet  than  any  other  incandescent  source,  and  which  failed 
completely  to  produce  any  specific  damage  to  the  eye,  although  in  one 
experiment  the  animal  was  overcome  by  the  general  heat  effect,  as  in 
sunstroke.  This  occurred  after  an  exposure  of  1|  hours  at  20  cm. 
from  the  filament.  A  second  experiment  with  an  exposure  of  2  hours 
at  the  same  distance,  in  which  the  animal  was  well  protected  from  the 
heat  and  the  head  kept  cooled  with  water,  showed  no  damage  to  the 
eye  of  any  kind.  This  source  as  a  whole  focusses  less  sharply  than 
does  the  arc  lamp  taking  an  equal  amount  of  energy,  and  in  this  case 
we  have  already  shown  that  the  retina  would  not  be  subject  to  damage 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         739 

save  by  an  impossibly  long  exposure  with  accurate  fixation.  These 
experiments  were  at  far  shorter  distances  and  consequently  of  enor- 
mously greater  intensities  than  any  which  could  be  found  with  such 
sources  as  illuminants,  and  we  may  hence  conclude  that  so  far  as 
general  effects  of  thermic  energy  are  concerned  no  source  used  for 
illuminating  purposes  is  capable  under  working  conditions  of  produc- 
ing any  observable  deleterious  results. 

Experiments  with  the  arc  lamp  are  crucial  because  this  source  is 
nearer  to  being  a  point  source  than  any  illuminant  of  similar  power 
and  hence  gives  much  sharper  concentration  of  energy  in  the  image. 
It  is  with  this  concentration  in  the  image  that  the  possible  damage  to 
the  retina  is  concerned.  Diffuse  sources  which  do  not  come  to  a 
definite  focus  may  be  entirely  neglected  for  this  particular  purpose. 
Low  temperature  sources  of  which  most  of  the  energy  lies  in  the  ex- 
treme infra  red  are  even  less  effective  in  concentrating  energy  upon 
the  retina,  because  the  eye  never  focusses  such  wave  lengths  on  the 
retina  except  as  a  diffuse  spot. 

The  only  sources  from  which  there  seems  to  be  any  material  danger 
from  the  standpoint  of  thermic  effects  are  certain  very  powerful  high 
temperature  sources  used  in  the  arts,  such  as  heavy  arcs  used  for 
welding  purposes,  furnaces,  electric  or  other,  where  there  is  customarily 
great  concentration  of  energy,  and  such  purely  accidental  phenomena 
as  short  circuits.  Perhaps  some  of  the  very  powerful  arcs  used  in 
searchlights  might  be  included  in  this  class  of  the  possibly  dangerous. 
Ordinary  discretion  in  avoiding  disagreeably  powerful  lights  or  suita- 
bly shading  the  eyes  from  them  should  avert  easily  all  real  danger 
from  any  of  these  sources  of  radiation,  save  the  short  circuits  which  are 
accidental  rather  than  ordinary  risks.  Certainly  no  sources  used  for 
lighting  purposes  can  be  classified  as  dangerous  from  the  standpoint 
of  thermic  effects. 

We  wish  particularly  to  emphasize  the  fact  that  so  far  as  any  possible 
temporary  or  permanent  injury  to  the  retina  is  concerned  such  action 
must  depend  on  the  concentration  of  energy  in  the  image.  Conse- 
quently, extended  sources  of  moderate  intrinsic  brilliancy  are  to  be 
preferred  to  intense  sources.  Hence  it  is  desirable  to  protect  all 
sources  naturally  of  high  intrinsic  brilliancy  by  diffusing  globes. 

As  regards  dangers  of  injury  to  the  eye  from  light  radiation  as  such, 
our  experiments  indicate  that  it  has  been  very  greatly  exaggerated 
as  regards  its  pathological  possibilities.  It  is  undoubtedly  true  that 
brilliant  sources  of  light  are  disagreeable  and  that  they  produce 
unpleasant  effects  in  temporary  scotomata,  disturbance  of  color 


740  VERHOEFF  AND   BELL. 

vision,  persistent  and  annoying  after  images  and  fatigue  due  to  efforts 
to  overcome  the  difficulties  of  vision  under  these  disadvantages.  As 
regards  definite  pathological  effects  or  permanent  impairment  of 
vision  from  exposure  to  the  luminous  rays  alone  we  have  been  unable 
to  find  either  clinically  or  experimentally  anything  of  a  positive  nature. 
The  experiments  on  monkeys,  which  we  have  recorded,  show  very 
clearly  that  exposure  to  light  of  intensity  many  times  greater  than 
anything  to  be  found  in  the  use  of  commercial  illuminants  produced 
only  temporary  scotomata.  The  lid  reflexes  appeared  within  a  very 
few  minutes  and  the  scotomata  seemed  to  have  worn  away  within  at 
most  a  few  hours.  There  was  not  the  slightest  sign  of  permanent 
impairment  of  vision.  As  noted  on  page  684  there  were  indications 
that  the  process  of  light  adaptation  may  go  on  to  a  considerable  degree 
even  during  very  severe  exposure  to  light.  In  the  experiments  on  the 
human  eye  results  were  found  closely  comparable  with  those  obtained 
in  the  earlier  experiments  on  monkeys.  The  erythropsia  passed  away 
in  a  few  minutes  and  the  scotoma  wore  away  rapidly  so  that  after 
three  hours  the  visual  acuity  was  normal,  although  there  still  remained 
traces  of  color  scotoma.  After  22  hours  visual  acuity  remained  normal 
and  the  central  color  vision  for  red,  blue  and  green  was  also  normal. 
This  intensity  of  the  light  in  this, case  was  far  in  excess  of  anything 
which  could  be  reached  in  the  use  of  commercial  illuminants  and 
there  was  a  length  of  fixation  many  times  greater  than  could  ever 
be  found  in  practical  use  of  lights.  These  experiments  seemed  con- 
clusive in  showing  that  the  effect  of  even  extraordinarily  severe 
exposure  to  luminous  rays  produces  only  such  temporary  effects  as 
might  reasonably  be  expected  and  is  followed  by  no  lasting  injuries 
of  any  kind.  Whether  frequent  and  long  exposures  of  a  similar  kind 
might  exhaust  the  extraordinary  recuperative  powers  of  the  eye  is  a 
matter  on  which  in  the  nature  of  things  there  can  be  no  direct  ex- 
perimental evidence  and  which  is  not  of  practical  importance  since 
under  no  working  conditions  could  even  a  single  exposure  compar- 
able in  severity  with  those  obtained  in  our  experiments  be  produced. 
There  is,  however,  very  strong  clinical  evidence  that  even  severe  daily 
exposures  to  intense  light  lasting  over  many  years  fails  to  produce 
material  injury  to  the  eye.  For  in  the  case  of  glass  blowers  there  is 
extreme  exposure  both  to  the  heat  and  light  of  the  furnace  occurring 
daily  for  many  years.  While  glass  blowers'  cataract,  probably  arising 
as  we  have  shown  from  secondary  causes  quite  aside  from  the  direct 
effects  of  radiation,  may  be  produced  under  these  circumstances, 
there  has  never  been  noted  any  injury  to  the  retina.  The  fact  that 


EFFECTS   OF   RADIANT   ENERGY   ON   THE   EYE.  741. 

the  retina  is  uninjured  under  these  extreme  conditions  seems  to  indi- 
cate as  do  our  experiments  that  the  eye  is  remarkably  tolerant  of 
intense  light  even  under  the  circumstances  of  exposures  of  great 
severity  lasting  over  very  long  periods  of  time. 

These  results  do  not  justify  the  use  of  powerful  unscreened  sources 
near  the  eye,  since  in  this  condition  vision  becomes  difficult  and  the 
effects  of  eye-strain  due  to  other  causes  than  mere  illumination  of  the 
retina  become  unpleasantly  in  evidence.  They  do  show,  however, 
that  the  eye  in  the  process  of  its  evolution  has  acquired  the  ability  to 
take  care  of  itself  under  extreme  conditions  of  illumination  to  a  degree 
hitherto  deemed  highly  improbable,  and  that  the  effects  on  the 
retina  due  to  any  exposure  to  intense  light  in  the  least  degree  likely  to 
be  found  in  the  use  of  practical  illuminants  are  temporary  and  of  no 
pathological  significance.  A  fortiori,  there  is  not  even  a  remote  chance 
of  pathological  effects  on  the  structure  of  the  eye  due  to  light  received 
from  extended  surfaces  of  low  intensity  like  translucent  globes  and 
diffuse  reflections  as  from  paper. 

As  for  the  ultra  violet  part  of  the  spectrum  to  which  exaggerated 
importance  has  been  attached  by  many  recent  writers,  the  situation 
is  much  the  same  as  with  respect  to  the  rest  of  the  spectrum,  that  is, 
while  under  conceivable  or  realizable  conditions  of  over  exposure 
injury  may  be  done  to  the  external  eye  yet  under  all  practical  condi- 
tions found  in  actual  use  of  artificial  sources  of  light  for  illumination 
the  ultra  violet  part  of  the  spectrum  may  be  left  out  as  a  possible 
source  of  injury.  All  illuminants  possess  an  easily  measurable  amount 
of  ultra  violet  radiation  ranging,  as  one  of  us  has  already  shown19 
from  about  4  ergs  per  second  per  square  cm.  per  foot  candle  of  illumi- 
nation in  the  quartz  arc  with  the  usual  globe,  to  more  than  twenty 
times  this  amount  in  the  enclosed  carbon  arc  shining  through  a  quartz 
window.  Between  these  two  lie  the  whole  range  of  incandescent  lamps 
both  gas  and  electric,  the  ordinary  mercury  arcs  and  the  ordinary 
Cooper  Hewitt  tube,  flames,  arc  lamps  of  various  sorts,  and  sunlight. 
The  last  mentioned  occupies  an  intermediate  position  between  the 
high  efficiency  electric  incandescent  lamps  and  the  older  incandescent 
lamps  or  ordinary  flames.  The  ultra  violet  in  these  various  sources 
is  distributed  in  different  ways.  All  the  flames  and  incandescents 
give  continuous  spectra  which  die  out  for  even  the  highest  tempera- 
ture of  these  sources  at  about  wave  length  300  /x/x.  Sources  giving 
discontinuous  spectra  generally  extend  below  this  limit  of  wave 
length,  but  often  with  very  feeble  radiation  in  this  region.  Such,  for 
instance,  is  the  case  with  the  carbon  arcs,  which  show  chiefly  metallic 


742  VERHOEFF   AND   BELL. 

impurity  lines  within  the  very  short  wave  lengths  and  owe  their 
considerable  proportion  of  ultra  violet  to  radiation  just  outside  the 
visible  spectrum.  From  the  standpoint  of  effects  upon  the  eye  the 
ultra  violet  region  may  be  divided  into  two  sharply  separated  portions, 
one  of  which  produces  abiotic  effects  while  the  other  does  not.  We 
have  for  the  first  time  definitely  established  the  line  of  partition 
between  these  two  portions  at  305  /J./JL.  Some  of  the  earlier  experi- 
menters in  this  field  imagined  that  they  had  detected  abiotic  effects 
with  slightly  longer  wave  lengths,  an  error  apparently  due  to  insuffi- 
cient knowledge  of  the  absorbing  screens  which  they  employed,  which 
with  rare  exceptions  are  described,  if  at  all,  in  very  loose  terms. 

No  injurious  effects  have  been  attached  with  any  reasonable  degree 
of  certainty  to  the  ultra  violet  radiation  which  lies  between  the  end 
of  the  visible  spectrum  and  the  beginning  of  the  abiotic  rays.  Since 
this  range  of  radiation  is  present  in  considerable  amount  in  ordinary 
sunlight,  it  is  sufficiently  obvious  that  any  definitely  harmful  results 
producible  under  ordinary  conditions  would  have  been  eliminated  by 
the  ordinary  progress  of  evolution.  Artificial  illuminants  under  any 
practical  conditions  of  use  expose  the  eye  to  much  less  severe  radia- 
tion in  this  part  of  the  spectrum  than  does  ordinary  daylight  and  a 
fortiori  can  be  excluded  as  possible  sources  of  harm. 

With  respect  to  abiotic  radiations  we  have  every  reason  to  acquit 
on  sound  experimental  basis  every  known  artificial  illuminant  when 
working  under  the  ordinary  conditions  of  commercial  use.  Even  the 
quartz  mercury  lamp,  which  is  per  se  richer  in  abiotic  radiations  than 
any  other  commercial  source  of  illumination,  when  equipped  with  its 
ordinary  globe  is  not  only  less  rich  in  ultra  violet  per  candle  power 
given  than  any  other  source,  but  is  as  we  have  found  by  experiment 
incapable  of  producing  any  abiotic  effects  on  the  eye  even  after  six 
hours  exposure  at  30  cm.  from  the  tube.  We  have  further  shown 
that  even  where  the  lamp  is  used  without  its  globe,  a  condition  which 
is  avoided  in  consideration  of  efficiency,  long  exposures  would  still  be 
necessary  to  produce  any  injurious  effects  at  any  distance  reasonably 
to  be  expected.  The  same  immunity  from  danger  attaches  to  all  the 
sources  at  present  in  commercial  use.  It  is  well  within  the  bounds 
to  say  that  there  is  no  commercial  illuminant  from  which  the  least  risk 
of  abiotic  radiation  is  incurred  under  the  circumstances  of  practical 
use.  The  only  sources  used  in  the  arts  which  have  abiotic  power 
enough  to  require  special  caution  in  their  use  are  those  not  employed 
for  the  purpose  of  illumination.  Such,  for  example,  are  the  powerful 
arcs  used  in  some  electric  welding  processes,  those  employed  in  the 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         743 

fixation  of  nitrogen  from  the  air  and  lamps  specifically  designed  for 
abiotic  purposes,  like  the  ultra  violet  lamp  of  Henri,  Helbronner  and 
de  Recklinghausen.164  The  last  mentioned  is  a  quartz  arc  of  peculiar 
form  taking  1150  watts  and  giving  approximately  six  times  as  much 
abiotic  radiation  as  the  lamp  used  in  our  experiments.  Such  a  source 
would  therefore  give  typical  photophthalmia  in  about  one  minute 
at  50  cm.  and  milder  symptoms  of  conjunctivitis  and  erythema  in 
somewhat  less  than  this  time.  A  comparable  degree  of  activity  is 
indicated  for  the  other  sources  here  referred  to.  In  these  cases  con- 
siderable caution  must  be  exercised  to  avoid  even  short  exposures  to 
the  unscreened  source,  but  arcs  of  this  character  are  highly  special 
in  their  functions  and  have  no  connection  with  matters  of  illumination. 

As  regards  the  general  effects  of  the  ultra  violet  portion  of  the  spec- 
trum, it  must  be  remembered  that  the  abiotic  action  is  chiefly  super- 
ficial and  we  have  shown  that  even  under  exposures  of  great  severity 
there  are  no  indications  of  any  injury  to  the  retina  from  ultra  violet 
rays  even  in  the  aphakic  eye. 

In  order  to  make  it  clear  that  the  results  as  to  abiotic  action,  which 
we  have  obtained  from  animal  experimentation,  are  substantially 
applicable  to  the  human  eye  as  well,  we  may  from  the  standpoint  of 
general  theory*  point  out  that  the  effect  of  the  abiotic  rays  we  have 
shown  to  be  definitely  dependent  on  the  quantity  of  the  radiation, 
the  action  of  which  can  be  reckoned  much  as  if  it  were  a  mere  mechani- 
cal force.  There  is  no  reason  from  our  experiments  or  those  of  others 
to  suppose  that  such  radiations  act  with  much  greater  intensity  on 
one  kind  of  living  cell  than  on  another.  We  have  in  addition  ample 
direct  evidence  that  the  effect  on  the  human  eye  and  on  the  rabbit's 
eye  are  entirely  comparable,  for  we  have  shown  experimentally  that 
the  critical  amount  of  abiotic  radiation  for  photophthalmia  on  the 
rabbit's  cornea  and  for  erythema  on  the  human  skin  is  the  same. 
As  a  clinical  fact,  of  which  the  early  observations  of  Charcot 15  are 
typical,  in  every  case  of  photophthalmia  the  erythema  of  the  skin 
surrounding  the  eye  is  quite  as  conspicuous  as  the  conjunctivitis. 
In  fact,  while  in  practically  every  case  of  photophthalmia  erythema 
appears,  it  is  very  rare  in  clinical  cases  to  find  the  stippling  of  the 
cornea  taken  as  one  of  our  characteristic  symptoms,  hence  the  amount 
of  abiotic  energy  required  to  produce  photophthalmia,  since  it  will 
also  produce  erythema,  must  be  substantially  as  great  for  the  human 
eye  as  for  the  rabbit's  eyes  on  which  most  of  our  experiments  were 
performed. 

Our  general  conclusion,  therefore,  regarding  the  effect  of  radiation 


744  VERHOEFF  AND   BELL. 

from  practical  illuminants  on  the  human  eye  is  that  no  sources  com- 
mercially employed  for  such  a  purpose  are  to  be  regarded  as  dangerous 
and  that  the  most  ordinary  care  in  providing  illumination  with  which 
comfortable  vision  can  be  obtained  is  sufficient  for  complete  security 
against  all  possibility  of  injury  from  radiation. 


PROTECTIVE  GLASSES. 

As  we  have  shown,  the  lens  completely  screens  the  retina  from 
abiotic  radiations  so  that  attempts  further  to  protect  it  from  such 
radiations  by  means  of  glasses  of  any  kind  are  superfluous.  We  have 
also  shown  that  the  retina  even  of  the  aphakic  eye,  under  ordinary 
conditions  is  in  no  danger  of  injury  by  any  source  of  light  in  common 
use,  and  is  no  doubt  completely  protected  by  the  thick  cataract  glasses 
usually  worn.  In  addition  we  have  shown  that  the  retina  under 
ordinary  conditions  is  in  no  danger  of  injury  from  the  heat  generated 
within  it  by  the  light  from  such  sources.  Heat  effects  are  to  be  feared 
only  in  the  case  of  extreme  light  intensities  such  as  direct  sunlight, 
and,  exceptionally,  short  circuit  arcs  and  lightning  flashes.  Against 
these  any  of  the  extremely  dark  glasses  are  effective. ' 

As  regards  the  external  eye,  as  just  pointed  out,  it  also  is  in  no  danger 
from  abiotic  radiations  from  any  of  the  usual  light  sources.  Photoph- 
thalmia  may  of  course  readily  be  produced  by  sufficiently  long  ex- 
posures at  close  range  to  high  power  arc  lights  of  any  kind,  or  to  the 
quartz  or  uviol  mercury  vapor  lamps,  but  it  is  only  under  special 
conditions  that  such  exposures  would  occur.  Here  ordinary  spectacles 
of  crown  glass  usually  afford  sufficient  protection,  and  adequate  pro- 
tection would  certainly  be  afforded  by  any  of  the  ordinary  yellowish, 
greenish  or  grayish  protective  glasses  in  common  use,  preferably  in 
the  form  of  coquilles  so  as  to  exclude  lateral  light.  These  would  also 
afford  ample  protection  against  snow  blindness  or  the  photophthalmia 
produced  by  short  circuits.  Birch-Hirschfeld  35  states  that  from  his 
own  personal  experience  in  protracted  and  regular  working  with  the 
uviol  lamp  he  found  complete  protection  from  photophthalmia  with 
the  smoke  gray  spectacles,  and  intimates  that  Stockhausen's  claim  of 
having  photophthalmia  after  working  with  the  electric  arc  lamp,  in 
spite  of  the  fact  that  he  wore  ordinary  spectacles,  is  readily  explained 
by  the  circumstances  that  common  spectacle  lenses  do  not  adequately 
protect  the  eye  from  radiation  entering  laterally. 

For  protection  of  the  external  eye  against  extreme  heat  such  as 


EFFECTS   OF   RADIANT   ENERGY  ON  THE   EYE.  745 

that  to  which  glass  blowers  are  exposed,  few  glasses  except  such 
special  ones  as  have  recently  been  devised  by  Crookes,  are  very 
effective,  the  deep  green  copper  oxide  glasses  being  perhaps  as  good 
as  any.  Such  glasses  combined  with  amber  or  yellow  green  tints  so 
as  to  reduce  the  transmitted  light  to  a  moderate  amount  in  the  middle 
of  the  spectrum  are  probably  the  most  efficient  protection  against 
extreme  radiation  of  all  kinds,  except  that  of  direct  sunlight.  In  the 
case  of  glass  blowers,  it  is  difficult  and  perhaps  futile  for  them  to  make 
use  of  any  sort  of  glasses,  owing  to  excessive  perspiration. 

So  far  then  as  concerns  actual  injury  by  light,  the  eye  under  ordi- 
nary conditions  of  modern  life  is  in  no  danger.  The  question  of  wear- 
ing protective  glasses  so  far  as  concerns  the  ordinary  individual  there- 
fore narrows  itself  down  to  the  determination  of  those  best  adapted  to 
obviate  the  sensations  resulting  from  too  intense  illumination.  These 
are  unpleasant  in  the  same  way  as  are  extremely  loud  noises,  and  for 
protection  against  them  one  wears  glasses  that  reduce  the  light  as  one 
plugs  the  ears  with  cotton  in  a  boiler  factory.  Any  glass  that  reduces 
the  light  is  effective  for  this  purpose,  but  preferably,  perhaps,  a  glass 
that  transmits  light  chiefly  in  the  middle  of  the  spectrum,  for  which  the 
eye  is  customarily  focussed.  The  question  of  the  color  of  the  glass  is, 
however,  of  little  importance  and  the  personal  idiosyncrasies  of  the 
individual  may  be  safely  allowed  free  play  here.  It  is  probable  that 
if  such  glasses  are  too  long  worn  they  will  increase  the  sensitiveness  of 
the  individual  to  light. 

The  question  of  the  use  of  protective  glasses  in  pathological  condi- 
tions of  the  eye  does  not  specially  concern  us  here,  but  it  may  be  stated 
that  it  is  one  simply  of  reducing  the  intensity  of  light  reaching  the 
retina.  In  cases  of  iritis  this  is  possibly  of  some  importance  since  it 
favors  dilatation  of  pupil.  In  cases  of  glaucoma,  on  the  other  hand, 
excess  of  light  is  desirable,  since  it  contracts  the  pupil.  As  Hess 18 
has  pointed  out,  the  sensations  incident  to  the  so  called  photophobia, 
associated  with  keratitis  and  other  irritable  conditions  of  the  eye,  are 
present  in  the  dark  as  well  as  in  the  light,  so  that  it  is  evident  that 
undue  importance  has  been  attached  to  the  exclusion  of  light  in  these 
conditions.  As  regards  fundus  conditions,  the  use  of  protective 
glasses  has  no  rational  basis,  except  possibly  in  the  case  of  retinitis 
pigmentosa  and  allied  conditions,  as  suggested  by  Axenfeld8. 

The  exaggerated  attention  that  has  been  paid  in  recent  years  to  the 
harmful  effects  of  ultra  violet  radiations  has  had  one  good  effect  in 
modifying  the  character  of  the  protective  glasses  prescribed  by 
ophthalmologists.  Earlier  practice  was  based  on  a  general  desire  to 


746  VERHOEFF   AND    BELL. 

cut  down  the  light  received  by  patients  whose  eyes  were  for  one  reason 
or  another  sensitive.  This  requirement  resulted  in  the  production 
of  glasses  of  more  or  less  dark  neutral  tints  and  sometimes  dark  shades 
of  colored  glasses  commercially  obtainable  like  green  and  blue.  A 
later  phase  of  practice  reflected  the  view  common  a  quarter  century 
ago  that  red  light  was  a  thing  producing  in  some  unknown  way  spe- 
cially bad  effects  and  consequently  was  to  be  shunned.  Hence  it  was 
not  uncommon  to  prescribe  glasses  of  cobalt  blue,  green,  and  various 
amethyst  tints.  It  is  interesting  to  note  that  such  glasses,  while  they 
reduce  greatly  the  red  of  the  visible  spectrum  still  transmit  quite 
freely  the  nearer  part  of  the  infra  red  which  carries  a  large  amount 
of  energy  (Coblentz76).  In  fact,  of  this  nearer  infra  red  such  glasses 
transmit  almost  as  much  as  does  ruby  glass.  Therefore,  the  earlier 
protective  glasses  were  not  effective  in  cutting  off  heat  radiation  and 
tended  to  transmit  mainly  light  toward  the  blue  end  of  the  spectrum. 
Perhaps  the  chief  benefit  of  the  agitation  that  has  taken  place  within 
the  last  decade  on  the  possible,  though  as  we  have  showTn  highly 
improbable  dangers  of  the  ultra  violet,  has  been  the  bringing  into 
prominence  the  new  types  of  protective  glasses. 

These,  intended  primarily  for  eliminating  the  ultra  violet  rays, 
have  tended  to  types  of  selective  absorption  which  give  advantageous 
results  in  modifying  the  visible  light,  which  is  really  the  chief  object 
of  concern  to  the  ophthalmologist.  There  is  a  close  kinship  in  the 
absorption  of  most  of  this  recent  crop  of  glasses.  The  prototype 
runs  back  nearly  twenty  years  to  the  work  of  Fieuzal 119  who  produced, 
specially  with  a  view  to  protecting  the  eye  against  glare  in  the  high 
mountains,  a  grayish  green  glass  which  cuts  off  the  ultra  violet  very 
completely  and  shades  down  the  blue  so  as  considerably  to  shorten 
the  spectral  range  of  the  rays  transmitted.  As  one  of  us  has  already 
shown18  the  last  line  transmitted  by  this  glass  from  the  spectrum 
of  the  quartz  arc  is  404.6  w  very  faintly.  Its  absorption  much 
resembles  (loc.  cit.)  that  of  ordinary  amber  glass,  except  that  the  latter 
carries  somewhat  heavier  absorption  into  the  blue  green  accounting 
for  its  yellowish  rather  than  greenish  tinge.  Either  of  these  glasses 
is  substantially  as  efficient  as  any  of  more  recent  origin  in  cutting 
out  the  ultra  violet.  In  more  recent  times  Hallauer 153  and  Schanz 
and  Stockhausen 309,  have  discussed  at  length  glasses  protective  against 
the  ultra  violet  and  have  brought  out  special  protective  glasses  with 
this  point  in  view,  the  former  known  by  the  name  of  the  inventor, 
the  latter  under  the  trade  designation  "  Euphos."  At  about  the  same 
period  the  firm  of  Rodenstock  produced  a  glass  of  similar  type  under 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         747 

the  trade  name  of  "Enixanthos"  and  various  approximations  to  and 
imitations  of  these  have  from  time  to  time  appeared.  A  paper  by 
Hallauer 155  gives  the  result  of  a  rather  thorough  spectrographic  study 
of  all  the  protective  glasses  then  in  common  use  to  which  those  inter- 
ested in  the  subject  may  be  referred.  The  composition  of  most  of 
these  glasses  is  held  as  an  unnecessarily  solemn  secret,  but  it  is  gener- 
ally understood  that  they  are  essentially  iron-lead  glasses.  They 
run  in  color  from  a  distinctly  yellowish  to  a  somewhat  bluish  green, 
varying  in  tone  and  transmissibility  according  to  the  composition 
of  the  various  shades  put  on  the  market.  An  ordinary  green  glass 
bottle  gives  in  the  spectrograph  about  the  same  absorption  as  the 
medium  densities  of  any  of  the  glasses  referred  to.  The  deeper  shades 
of  any  of  them  cut  off  the  spectrum  completely  just  about  at  the 
beginning  of  the  ultra  violet  and  weaken  it  well  into  the  violet.  The 
lighter  shades  transmit  to  wave  lengths  360  nn  to  320  ju/i  with  cor- 
respondingly less  reduction  in  the  general  intensity.  Any  and  all  of 
them  are  completely  effective  against  the  abiotic  radiations,  even 
although  the  medium  shades  sometimes  transmit  very  weakly  in  the 
region  3200  ju/x  to  3400  fj./j,  as  well  as  in  the  visible  spectrum.  To  render 
the  record  of  these  recent  protective  glasses  fairly  complete  there  is 
shown  in  Plate  7  the  iron  arc  spectrum  and  its  transmission  through 
the  three  ordinary  grades  of  the  Hygat  glass  of  Rodenstock,  an  excellent 
type  of  this  general  group.  Figure  6  is  here  the  iron  arc  spectrum, 
5,  4,  and  3,  respectively  the  light,  medium  and  dark  Hygat  glasses, 
and  Figure  1  a  special  protective  glass  of  American  manufacture 
designed  specifically  to  reduce  the  red  end  of  the  spectrum  beside 
cutting  out  the  ultra  violet  and  much  of  the  violet  and  blue.  In  point 
of  effectiveness  in  cutting  out  the  ultra  violet  the  differences  between 
these  various  glasses  of  approximately  the  same  shade  are  inconse- 
quential and  the  choice  between  them  lies  mainly  in  the  matter  of 
taste  as  regards  their  particular  color  and  absorption  in  the  visible 
part  of  the  spectrum.  Of  the  recent  glasses  exploited  in  America  the 
so  called  Noviol  glass  is  remarkable  for  its  extraordinarily  sharp  cut 
off  of  the  spectrum  in  the  blue. 

Voege388  in  answering  the  question  as  to  what  spectral  range  of 
radiation  gave  the  most  satisfactory  results  held  that  the  light  from 
the  clouds  of  a  clear  sky,  being  that  light  to  which  the  eye  through 
evolution  had  become  adapted,  was  on  the  whole  to  be  preferred. 
This  would  indicate  the  use  of  neutral  glasses  without  selective  absorp- 
tion. Hertel  and  Henker172  found  that  clouds  and  clear  sky  con- 
tain very  little  energy  below  310  /JL/JL  and  considered  that  the  only 


748  VERHOEFF  AND   BELL. 

protection  needed  for  artificial  light  sources  was  to  reduce  the  light 
from  them  at  the  working  distance  to  substantially  the  range  of  the 
sky  spectrum.  From  these  and  other  experiments  they  concluded 
that  the  best  protective  glass  should  preferably  reduce  the  spectrum 
to  approximately  that  of  cloud  or  sky  light.  This  again  indicates 
the  use  of  neutral  non  selective  absorbing  glasses.  Against  this  view 
it  may  be  properly  objected  that  the  eye  in  its  evolution  has  rejected 
the  whole  infra  red  and  ultra  violet  as  ineffective  and  in  fact  derives 
very  little  useful  illumination  from  the  red  at  the  one  end  and  the 
violet  and  blue  at  the  other.  The  luminosity  values  of  these  portions 
of  the  spectrum  are  very  small  and  it  may  be  added,  fortunately  very 
small,  else  the  chromatic  aberration  of  the  eye  would  make  distinct 
vision  quite  impossible.  We  are  inclined,  therefore,  rather  to  the 
view  that  such  radiation  as  produces  the  maximum  required  lumi- 
nosity with  the  minimum  energy  access  to  the  eye  is  best  adapted  to 
protect  the  eye  from  any  and  all  injuries  which  may  be  due  to  exces- 
sive radiation.  This  indicates  the  use  of  glasses  absorbing  at  both  ends 
of  the  spectrum  so  as  to  bring  the  strongest  light  in  the  region  of  great- 
est luminosity,  that  is  in  the  yellow  green.  As  one  of  us  has  already 
shown 18  composite  spectacles  reducing  the  spectrum  to  a  nearly 
monochromatic  stripe  in  this  region  actually  enable  one  to  view  the 
most  powerful  sources  without  discomfort  while  yet  transmitting 
enough  light  to  permit  writing  or  reading  one's  notes.  The  glasses 
of  Plate  7  in  the  deeper  shades  all  show  something  of  this  character- 
istic absorbing  both  ends  of  the  spectrum  and  in  so  far  represent 
a  slightly  different  type  from  the  glasses  which  have  preceded  them. 
Crookes  found  that  suitable  absorption  at  both  ends  of  the  spectrum 
could  not  be  obtained  without  encroaching  somewhat  on  the  visible 
portion  but  rendered  this  encroachment  rather  inconspicuous  by  using 
a  heavy  didymium  glass  which  cuts  out  the  yellow  and  leaves  a 
pinkish  tinge.  This,  however,  is  not  an  objection  in  cases  requiring 
thorough  protection  unless  the  encroachment  is  so  great  as  actually 
to  be  inconvenient  in  seeing.  Where,  therefore,  practical  protection 
against  powerful  sources  of  radiation  is  necessary,  glasses  meeting  the 
requirement  of  maximum  luminosity  with  minimum  energy  present 
material  advantages.  These  advantages  become  practically  inconse- 
quential where  the  question  is  one  of  merely  moderately  reducing  too 
bright  general  light,  and  the  choice  between  such  special  protective 
media  and  ordinary  neutral  tint  glass  reverts  again  to  a  matter  of 
taste. 


ULTRAVIOLET  LIGHT  AS  A  GERMICIDAL  AGENT. 
EXPERIMENTAL  INVESTIGATION  OF  ITS  POSSIBLE  THERAPEUTIC  VALUE.* 

F.  H.  VERHOEFF,  A.M.,  M.D. 

As  is  well  known,  light-waves  of  sufficiently  short  wave-lengths  are 
highly  germicidal  to  bacteria  suspended  in  mediums  which  are  trans- 
parent to  these  waves.  The  question  has  arisen,  therefore,  whether 
or  not  it  may  be  possible  to  make  use  of  ultraviolet  light  in  the  treat- 
ment of  local  infections. 

Ultraviolet  light  has  long  been  successfully  used  by  Finsen  in  the 
treatment  of  certain  skin  diseases,  notably  lupus  vulgaris,  and  re- 
cently has  been  employed  by  ophthalmologists  in  the  treatment  of 
vernal  catarrh  and  trachoma,  also,  it  is  asserted,  with  successful  results. 
Its  beneficial  effect  in  these  conditions,  however,  obviously  is  not 
necessarily  due  to  a  direct  germicidal  action,  but  possibly  only  to  an 
irritant  action  on  the  tissues. 

Since  the  cornea  compared  to  other  tissues  of  the  body  is  relatively 
transparent  to  ultraviolet  light,  it  follows  that  if  it  should  prove  im- 
possible by  this  means  to  destroy  bacteria  within  corneal  tissue  without 
at  the  same  time  producing  undue  injury  to  the  tissue  itself,  the  same 
negative  results  would  be  obtained  in  the  case  of  all  other  tissues. 
For  this  reason  the  present  investigation  was  confined  to  experiments 
on  the  cornea.  These  experiments  were  made  in  connection  with  an 
investigation  by  Louis  Bell  and  myself  on  the  effect  of  ultraviolet 
light  on  the  normal  eye,  advantage  being  taken  of  the  powerful  light 
sources  and  apparatus  therein  employed. 

Hertel l,  in  1903,  reported  the  successful  use  of  ultraviolet  light  in 
the  treatment  of  corneal  ulcers,  asserting  that  here  it  had  a  direct 
germicidal  action  on  the  infecting  bacteria.  He  also  made  some 
interesting  experimental  observations  in  this  connection,  the  most 
important  one  from  a  therapeutic  point  of  view  being  that  he  was  able 
to  abolish  the  motility  of  cholera  bacilli  enclosed  in  a  quartz  cell  and 

*  Reprinted  by  permission  from  the  Journal  of  the  American  Medical  Asso- 
ciation, March  7,  1914,  Vol.  LXII,  pp.  762-764. 

1  Hertel,  E.:  Experimentelles  iiber  ultraviolettes  Licht,  Ber.  ii.  d.  31  Vers. 
-d.  ophth.  Ges.,  Heidelberg,  1903,  p.  144. 

749 


750  VERHOEFF  AND  BELL. 

placed  within  the  anterior  chamber  of  a  rabbit's  eye,  by  exposing  them 
to  the  action  of  ultraviolet  light  passing  through  the  cornea.  The 
source  of  the  light  was  a  magnesium  electrode  giving  off  rays  with 
wave-lengths  from  0.28  to  0.309  microns,  and  the  exposures  were  from 
twenty-five  to  thirty  minutes.  The  current  was  from  3  to  4  amperes. 
Later  he  obtained  the  same  result  with  his  cadmium-zinc  electrode. 
Hertel  assumed  that  the  bacteria  were  actually  killed,  but  he  did  not 
state  that  this  was  demonstrated  by  means  of  cultures.  He  also  did 
not  exclude  the  possibility  that  the  effect  on  the  bacilli  was  due  to  heat. 

Hertel,  in  addition,  tested  the  therapeutic  action  of  ultraviolet 
light  on  a  series  of  rabbits'  eyes  in  which  he  had  produced  staphy- 
lococcic  corneal  ulcers  and  obtained  "  pleasing  results."  The  resulting 
scars  were  slight  and  no  changes  could  be  found  in  the  depths  of  the 
eyes.  These  results,  however,  it  seems  to  me,  lose  any  possible 
significance  when  it  is  considered  that  staphylococcic  corneal  ulcers 
artificially  produced  in  rabbits  as  a  rule  promptly  heal  without  any 
treatment,  as  I  have  frequently  observed. 

Hertel  maintains  that  light  of  short  wave-lengths  has  a  greater 
deleterious  effect  on  bacteria  than  on  tissue-cells.  This  may  be  true 
for  very  short  waves,  but  it  is  certainly  not  true  for  waves  which  are 
able  to  pass  through  the  cornea.  Thus,  I  found  that  severe  keratitis 
could  be  produced  by  exposing  the  cornea  through  a  crown  screen  to  a 
quartz  mercury-vapor  lamp  at  a  distance  of  20  cm.  for  one  and  one- 
half  hours,  whereas  staphylococci  suspended  in  distilled  water  and 
exposed  under  the  same  conditions  were  not  killed  in  six  hours2. 
This  experiment  also  would  seem  almost  alone  sufficient  to  prove  the 
impossibility  of  destroying  bacteria  within  the  clear  cornea  without 
producing  too  much  injury  to  the  corneal  cells.  This  being  the  case, 
it  is  almost  inconceivable  that  bacteria  could  be  destroyed  in  a  cornea, 
infiltrated  with  pus-cells  and  so  made  practically  impassable  to  germi- 
cidal  waves. 

Hertel  also  attached  importance  from  a  therapeutic  point  of  view 
to  the  conjunctival  hyperemia  and  cell  irritation  produced  by  ultra- 
violet light.  The  practical  value  of  these  factors  is  questionable,  and 
the  latter  factor  would  seem  more  likely  to  do  harm  than  good  in  the 
case  of  corneal  ulcers  in  which  the  cells  already  have  sufficient  un- 


2  It  is  important  to  note  that  for  these  long  exposures  it  is  necessary  to  keep 
the  bacterial  container  surrounded  by  cool  water,  as  otherwise  the  bacteria 
may  be  killed  in  an  hour  or  so  by  the  accumulated  heat.  The  lamp  and 
screen  used  in  this  experiment  are  described  later. 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         751 

favorable  influences  to  contend  with.  In  any  case  they  would  not 
justify  the  use  of  ultraviolet  light  in  treatment  of  such  conditions  in 
the  absence  of  any  germicidal  effect  of  the  light. 

In  a  later  communication,  Hertel3  reported  in  detail  a  series  of 
clinical  cases  of  corneal  ulcer  treated  by  means  of  ultraviolet  light 
from  a  cadmium-zinc  electrode.  The  latter  he  recommended  as  being 
equal  in  efficiency  to  the  magnesium  electrode  and  at  the  same  time 
more  practical  to  use.  Twenty-six  cases  were  treated  with  light 
therapy  alone,  8  cases  with  light  therapy  followed  by  Saemisch  section, 
and  13  cases  with  light  therapy  followed  by  cauterization  or  the  latter 
and  Saemisch  section.  Thus  in  21  out  of  his  47  cases  of  corneal  ulcer, 
the  result  of  the  light  therapy  was  so  unsuccessful  that  cauterization 
or  Saemisch  section  had  to  be  undertaken.  These  results  do  not 
seem  impressive  for  an  agent  that  is  supposed  to  kill  the  bacteria 
within  the  ulcers.  Hertel  exposed  his  patients  from  three  to  five 
minutes  two  or  three  times  daily.  At  the  most  this  was  equivalent  to 
a  daily  total  exposure  of  only  fifteen  minutes.  Now  he  had  found 
that  it  required  from  twenty-five  to  thirty  minutes  to  kill  (or  inhibit)  ? 
bacteria  exposed  through  a  perfectly  clear  cornea.  How  then  could 
it  be  expected  that  an  exposure  of  fifteen  minutes  would  suffice  to  kill 
them  in  a  purulent  infiltrate  which  acts  as  a  far  more  effective  barrier 
to  ultraviolet  light? 

In  a  communication  to  appear  later,  Louis  Bell  and  I  show  that 
interrupted  exposures  to  ultraviolet  light  with  intervals  of  less  than 
twenty-four  hours  have  practically  the  same  effect  on  the  cornea  as  a 
continuous  exposure  of  the  same  total  length.  For  this  reason  by 
frequently  repeating  his  exposures,  Hertel  undoubtedly  increased 
the  injury  to  the  corneal  tissue  without  at  the  same  time,  in  all  proba- 
bility, obtaining  a  corresponding  increase  in  germicidal  action. 

In  his  experiments  and  in  the  treatment  of  his  cases  Hertel  employed 
no  screens.  Thus  the  cornea  had  not  only  to  contend  with  the  rays 
that  could  penetrate  it,  but  also  with  those  stopped  within  the  stronia 
and  at  the  surface.  As  the  rays  stopped  near  the  surface  are  evi-, 
dently  useless  so  far  as  killing  bacteria  within  the  stroma  is  concerned 
it  occurred  to  me  that  by  screening  them  out  and  so  decreasing  the 
damage  to  the  cornea,  longer  exposures  might  safely  be  used,  thereby 
increasing  the  possibility  of  a  germicidal  effect  within  the  cornea. 
The  screen  selected  for  this  purpose  was  a  crown  glass,  which  permitted 

3  Hertel,  E.:  Experimentelles  und  klinisches  iiber  die  Anwendung  lokaler 
Lichttherapie  bei  Erkrankungen  des  Bulbus,  Arch.  f.  Ophth.,  1907,  Ixvi,  No.  2, 
p.  275. 


752  VERHOEFF  AND  BELL. 

only  waves  greater  than  0.295  microns  in  length  to  pass  4.  As  will 
be  seen,  however,  this  procedure  was  unsuccessful.  No  germicidal 
effect  on  bacteria  within  the  cornea  could  be  noted  even  when  exposures 
through  this  screen  were  used  which  were  sufficient  to  produce  severe 
keratitis  and  even  injure  the  epithelium  of  the  lens  capsule. 

As  light  sources  in  the  following  experiments  the  magnetite  arc  and 
the  quartz  mercury-vapor  lamp  were  chiefly  used.  To  obviate  the 
remote  possibility  that  the  cadmium-zinc  arc  employed  by  Hertel 
might  possess  some  special  advantage,  this  arc  was  also  used.  That 
greater  intensity  was  obtained  with  our  cadmium-zinc  arc  and  quartz 
lens  than  was  obtained  by  Hertel  is  proved  by  the  fact  that  not  only 
severe  keratitis  but  also  marked  changes  in  the  epithelium  of  the  lens 
capsule  were  produced. 

The  mercury-vapor  lamp  used  was  the  Cooper-Hewitt  model  with- 
out the  globe  (220  volts,  3.5  amperes). 

The  magnetite  arc  was  of  the  ordinary  self-regulating  type  as  known 
to  trade,  without  the  globe.  The  voltage  was  about  80,  the  amperage 
from  9.8  to  10.  The  light  was  passed  through  a  quartz  water-cell 
5  cm.  in  thickness,  and  concentrated  on  the  cornea  by  means  of  a 
quartz  lens  4  cm.  in  diameter  and  9  cm.  in  focal  length,  placed  20  cm. 
from  the  light  source.  In  Experiments  6  and  7  still  greater  intensity 
was  obtained  by  means  of  a  second  quartz  lens  23  mm.  in  diameter 
and  15  mm.  in  focal  length. 

In  the  case  of  the  cadmium-zinc  arc,  the  same  apparatus  was  used 
except  that  the  electrode  consisted  of  an  alloy  of  equal  parts  of  cad- 
mium and  zinc  in  a  thin-walled  copper  cylinder,  and  was  water-cooled. 
The  water-cell  was  omitted.  The  voltage  was  about  80,  the  amperage 
about  6.8. 

A  number  of  experiments  were  first  made  by  injecting  staphylo- 
cocci  or  pneumococci  into  the  corneas  of  rabbits  and  after  twenty-four 
hours  exposing  the  resulting  abscesses  to  the  ultraviolet  light.  Healing 
did  not  seem  to  be  hastened,  but  since  recovery  ultimately  occurred, 
as  it  did  also  in  the  control  eyes,  these  experiments  are  not  regarded 
as  sufficiently  conclusive  and  are  not  given  in  detail.  Experiment  1, 
however,  in  which  tubercle  bacilli  were  injected  into  the  cornea,  was 


4  Since  this  wave-length  has  been  found  to  be  the  limit  of  transparency  for 
the  cornea,  it  would  be  expected  that  such  a  screen  would  protect  the  cornea 
from  injury,  the  longer  waves  not  being  absorbed  by  the  latter.  As  a  matter 
of  fact  I  have  found  that  it  does  almost  completely  protect  the  corneal  stroma, 
but  permits  severe  injury  or  destruction  of  the  epithelium,  corneal  corpuscles 
and  endothelium. 


EFFECTS   OF  RADIANT   ENERGY   ON   THE   EYE.  753 

perfectly  conclusive  since  the  resulting  lesions  continued  to  progress 
in  both  eyes  alike.  In  the  other  experiments  the  exposures  were  made 
immediately  after  the  injections,  that  is,  with  the  corneas  clear,  so 
that  the  conditions  were  the  most  favorable  possible  for  germicidal 
action  of  the  light.  The  results  in  these  experiments,  moreover, 
are  clear-cut,  because  if  the  light  had  killed  the  bacteria,  abscesses 
would  not  have  formed.  This  is  proved  by  Experiment  2,  in  which 
in  the  control  eye  the  bacteria  were  first  killed  by  exposure  to  ultra- 
violet light  before  they  were  injected  into  the  cornea. 


EXPERIMENTS. 

Experiment  1.  April  10,  1912,  a  suspension  of  virulent  tubercle 
bacilli  is  injected  into  each  cornea  of  a  rabbit. 

May  1,  each  cornea  shows  a  small  tubercle.  The  right  eye  is  ex- 
posed to  the  quartz  mercury-vapor  lamp  through  crown  screen  1^ 
hours  at  20  cm. 

May  21,  both  tubercles  have  developed  as  usual.  The  animal  is 
killed. 

Experiment  2.  June  22,  1912,  a  suspension  of  Staphylococcus 
aurcus  in  distilled  -water  is  injected  superficially  into  the  left  cornea 
of  a  rabbit.  The  remaining  bacterial  suspension  is  then  exposed  at 
20  cm.  for  three  minutes  to  the  quartz  mercury-vapor  lamp.  (Cul- 
ture taken  proves  that  all  organisms  have  been  killed.)  This  suspen- 
sion of  killed  staphylococci  is  then  injected  into  the  right  cornea  of 
the  same  rabbit. 

Each  cornea  is  exposed  to  the  quartz  mercury-vapor  lamp  at  a  dis- 
tance of  0.5  meter  for  fifteen  minutes. 

June  23,  both  eyes  show  marked  photophthalmia.  The  left  cornea 
shows  well-marked  abscess.  The  right  cornea  shows  only  a  faint  haze 
along  the  tract  of  the  needle. 

June  24,  both  eyes  show  increase  in  photophthalmia,  with  haze  of 
corneal  stroma  and  central  loss  of  corneal  epithelium.  The  abscess  of 
the  left  cornea  has  increased  in  size  and  there  is  now  hypopion.  The 
right  cornea  shows  no  abscess.  Enucleation  is  performed. 

Experiment  3.  Oct.  21,  1913,  a  suspension  of  Staphylococcus 
aurcus  in  distilled  water  is  injected  into  each  cornea  of  a  rabbit,  the 
amount  injected  into  the  right  cornea  being  three  times  that  injected 
into  the  left.  The  left  eye  is  then  exposed  for  thirty  minutes  to  the 


754  VERHOEFF  AND   BELL. 

cadmium-zinc  arc  through  a  quartz  lens  (no  water-cell  or  screen  of 
any  kind  being  used). 

October  22,  the  right  eye  shows  intense  inflammatory  reaction,  with 
a  large  abscess  of  the  cornea  and  pus  in  the  anterior  chamber.  The 
left  eye  shows  equally  intense  inflammatory  reaction  and  a  corneal 
abscess  about  half  the  size  of  that  in  the  right  cornea.  The  abscess 
shows  discrete  points  evidently  corresponding  to  colonies  of  bacteria. 

October  23,  abscesses  of  the  two  corneas  are  now  about  equal  in 
size,  (3  mm.  in  diameter).  The  anterior  chamber  of  each  eye  contains 
pus.  Epithelium  is  entirely  absent  from  the  left  cornea  (this  being 
confirmed  by  microscopic  examination) .  The  right  cornea  shows  loss 
of  epithelium  only  in  the  vicinity  of  the  abscess.  Enucleation  is 
performed. 

The  lens  capsule  of  the  right  eye  after  fixation  in  Zenker's  fluid  is 
examined  in  flat  preparation  and  shows  slight  changes  in  the  nuclei  of 
the  epithelium  evidently  due  to  the  action  of  staphylococcus  toxins, 
but  no  changes  similar  to  those  seen  after  exposure  to  ultraviolet  light. 
The  lens  capsule  of  the  left  eye  shows,  in  addition  to  these  nuclear 
changes,  well-marked  changes  characteristic  of  exposure  to  ultraviolet 
light  —  swelling  and  granular  degeneration  of  the  cytoplasm  of  the 
epithelial  cells.  Histologically  both  corneas  present  the  same  picture, 
and  each  contains  numerous  large  masses  of  staphylococci. 

Experiment  4.  Feb.  8,  1913,  a  suspension  of  Staphylococcus  aureus 
in  distilled  water  is  injected  into  each  cornea  of  a  rabbit.  The  left 
cornea  is  then  exposed  for  thirty  minutes  to  the  cadmium-zinc  arc 
through  a  crown  screen  and  quartz  lens,  the  image  being  kept  on  the 
injected  area. 

February  10,  there  are  abscesses  of  equal  size  in  the  two  corneas. 
The  left  eye  in  addition  shows  severe  photophthalmia  with  marked 
general  haze  of  cornea  and  large  central  loss  of  epithelium  which  in- 
cludes area  of  abscess.  This  eye  also  shows  exudate  adherent  to 
the  posterior  surface  of  the  cornea  behind  the  site  of  the  abscess, 
due  evidently  to  injury  of  the  endothelium  by  the  ultraviolet  light. 
Enucleation  is  performed. 

The  lens  capsule  of  the  left  eye,  after  fixation  in  Zenker's  fluid,  is 
examined  microscopically  in  flat  preparation,  and  shows  marked 
changes  characteristic  of  exposure  to  ultraviolet  light. 

Experiment  5.  March  19,  1913,  a  suspension  of  Staphylococcus 
aureus  in  distilled  water  is  injected  into  the  cornea  of  a  rabbit.  The 
cornea  is  then  exposed  to  the  magnetite  arc  for  forty-five  minutes 
through  the  quartz  lens,  quartz  water-cell,  and  crown  screen.  This 
•exposure  in  the  case  of  normal  eyes  had  been  found  sufficient  to  cause 


EFFECTS   OF   RADIANT   ENERGY  ON  THE   EYE.  755 

necrosis  of  the  stroma  cells  and  endothelium  of  the  cornea,  to  cause 
hemorrhages  in  the  iris,  and  to  produce  marked  changes  in  the  lens 
capsular  epithelium. 

March  20,  there  is  abscess  of  the  cornea.  Marked  photophthalmia 
is  noted  with  loss  of  epithelium. 

March  24,  the  abscess  is  larger.     Enucleation  is  performed. 

Lens  capsular  epithelium  (flat  preparation)  on  microscopic  exami- 
nation shows  marked  changes,  and  the  iris  shows  numerous  hemor- 
rhages characteristic  of  exposure  to  ultraviolet  light. 

Experiment  6.  Dec.  16,  1913,  a  suspension  of  Staphylococcus 
aureus  in  distilled  water  is  injected  into  the  cornea  of  a  rabbit.  The 
injected  area  is  then  exposed  twenty  minutes  to  the  magnetite  arc 
through  a  water-cell  and  a  system  of  two  quartz  lenses.  No  screen 
is  used. 

As  previously  determined,  with  this  arrangement  an  exposure  of 
thirty  seconds  is  sufficient  to  cause  marked  keratitis  and  destruction 
of  the  epithelium,  while  an  exposure  of  twenty  minutes  causes  com- 
plete destruction  of  the  corneal  corpuscles  and  softening  and  swelling 
of  the  stroma  down  to  Descemet's  membrane,  and  ultimately  leads  to 
vascularization  and  cicatrization  of  the  cornea. 

December  18,  there  is  no  abscess.  Marked  photophthalmia  is  noted. 
The  cornea  is  hazy  and  epithelium  is  absent  from  three  quarters  of  the 
surface  of  the  cornea. 

December  26,  there  is  no  abscess.  The  inflammatory  reaction  is 
almost  gone.  The  cornea  is  softened  and  swollen. 

December  29,  the  inflammatory  reaction  is  increasing  again  (reaction 
of  repair);  the  corneal  tissue  is  very  soft.  Vascularization  is  well 
advanced. 

Jan.  5,  1914,  vascularization  of  the  cornea  is  complete.  The  in- 
flammatory reaction  is  subsiding. 

January  9,  the  vessels  are  beginning  to  disappear.  The  cornea  is 
leukomatous. 

Experiment  7.  Dec.  19,  1913,  the  suspension  is  injected  and  the 
exposure  made  as  in  Experiment  6,  except  that  the  time  of  exposure 
is  six  minutes.  This  exposure  is  sufficient  to  cause  softening  of  the 
corneal  stroma. 

December  21,  marked  photophthalmia  is  noted.  There  is  an 
abscess  at  the  site  of  the  injection. 

December  23,  the  abscess  is  smaller.  A  culture  is  taken.  Enu- 
cleation is  performed. 

Culture  shows  abundant  growth  of  staphylococci.  Lens  capsular 
epithelium  shows  marked  changes. 


756  VEKHOEFF   AND   BELL. 


CONCLUSIONS. 

The  results  of  these  experiments  prove  conclusively  that  ultraviolet 
light  cannot  under  any  conditions  destroy  bacteria  within  the  cornea, 
even  when  the  latter  is  perfectly  transparent,  without  at  the  same  time 
severely  injuring  the  corneal  tissue.  Destruction  of  bacteria  within 
the  transparent  cornea  was  obtained  only  when  a  light  intensity  and 
exposure  were  employed  sufficient  to  cause  complete  destruction  of 
the  corneal  corpuscles  and  intense  injury  to  the  corneal  lamellae 
(Experiment  6). 

Moreover,  it  does  not  seem  possible  that  ultraviolet  light  could  in 
practice  be  successfully  used  to  destroy  bacteria  within  a  corneal 
abscess  or  ulcer,  that  is,  when  the  cornea  was  no  longer  clear,  even 
with  the  sacrifice  of  corneal  tissue,  as  in  the  case  of  the  actual  cautery. 
For  either  the  exposures  would  have  to  be  impracticably  prolonged, 
or  such  extreme  intensity  of  light  would  be  required  that  the  heating 
effect  would  exceed  that  of  the  abiotic  action.  It  is  doubtful  also  if 
ultraviolet  light  of  such  intensity  could  be  made  available  for  thera- 
peutic purposes. 

It  must  be  concluded,  therefore,  that  so  far  as  direct  destruction 
of  bacteria  within  any  of  the  tissues  of  the  body  is  concerned,  ultra- 
violet light  possesses  no  therapeutic  value. 


GENERAL  CONCLUSIONS. 

1.  The  liminal  exposure  capable  of  producing  photophthalmia  to 
the  extent  of  conjunctivitis  accompanied  by  stippling  of  the  cornea, 
is  in  terms  of  energy  about  2  X  106  erg  seconds  per  square  cm.  of 
abiotic  radiation  of  the  character  derived,  for  example,  from  the  quartz 
lamp  or  the  magnetite  arc.  About  two  and  a  half  times  this  exposure, 
i.  e.,  5  X  106  erg  seconds  per  square  cm.  is  required  to  produce  loss 
of  corneal  epithelium. 

3.  The  abiotic  action  of  the  cornea  and  conjunctiva  produced  by 
any  radiating  sources  follows  the  law  of  inverse  squares  and  is  directly 
proportional  to  the  total  abiotic  energy  received.  It  can  therefore 
be  definitely  predicted  from  the  physical  properties  of  the  source. 

3.     After  exposure  of  the  eye  to  abiotic  radiations  there  is  a  latent 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         757 

period  before  any  effects  clinical  or  histological  become  perceptible. 
This  period  of  latency  in  a  general  way  varies  inversely  with  the 
severity  of  the  exposure,  but  a  theoretical  latency  of  24  hours  or  more 
corresponds  to  an  exposure  entirely  subliminal. 

4.  The  combined  effect  of  repeated  exposures  to  abiotic  radiations 
is  equivalent  to  that  of  a  continuous  exposure  of  the  same  total  length, 
provided  the  intermissions  are  not  long  enough  to  establish  reparative 
effects.     Approximately  the  exposures  are  additive  for  intermissions 
of  somewhat  less  than  24  hours.     Exposures  of  3  the  liminal  given 
daily  begin  to  show  perceptible  effect  after  about  6  exposures.     Daily 
exposures  of  g  the  liminal  repeated  over  long  periods  produce  no  effect 
whatever,  except  to  give  the  external  eye  a  degree  of  immunity  against 
severer  exposures.     Actual  abiotic  damage  to  the  external  eye  renders 
it  temporarily  more  sensitive  to  abiotic  action. 

5.  Abiotic  action  for  living  tissues  is  confined  to  wave  lengths 
shorter  than  305  H/JL,  at  which  length  abiotic  effects  are  evanescent, 
while  for  shorter  wave  lengths  they  increase  with  considerable  rapidity. 

6.  For  the  quartz  arc  and  the  magnetite  arc  the  abiotic  activity 
of  the  rays  absorbed  by  the  cornea  is  eighteen  times  greater  than  those 
which  are  transmitted  by  it.     To  affect  any  media  back  of  the  cornea 
requires  therefore  at  least  eighteen  times  the  liminal  exposure  hereto- 
fore mentioned. 

7.  Even  with  exposures  as  great  as  one  hundred  and  fifty  times  the 
liminal  for  photophthalmia  the  lens  substance  is  affected  to  a  depth 
of  less  than  20  p,  and  this  superficial  effect  undergoes  in  the  rabbit 
complete  repair.     Such  enormously  intensive  exposures,  which  we 
obtain  with'  the  magnetite  arc  and  double  quartz  lens  system  may 
completely  destroy  the  corneal  epithelium,  corpuscles,  and  endothe- 
lium.     The  corneal  stroma  may  be  strongly  affected  by  waves  shorter 
than  295  /J./JL,  which  it  completely  absorbs,  but  is  very  slightly  affected 
by  the  remaining  abiotic  radiation. 

8.  The  histological  changes  produced  by  abiotic  radiation  are 
radically  different  from  those  produced  by  heat,  and  the  cell  changes 
are  best  seen  in  flat  preparations  of  the  lens  capsule.     The  most  char- 
acteristic change  is  the  breaking  up  of  the  cytoplasm  into  eosinophilic 
and  basophilic  granules. 

9.  Changes  in  the  lens  epithelium  like  those  following  abiotic 
action,  including  the  formation  of  a  "wall"  beneath  the  pupillary 
margin,  are  not  exclusively  characteristic  of  abiotic  action,  but  may 
be  produced  by  ordinary  chemical  reagents.     They  are,  therefore, 
characteristic  not  of  abiotic  action  alone,  but  of  chemical  action  in 
general. 


758  VERHOEFF  AND   BELL. 

10.  Abiotic  radiations  certainly  do  not  directly  stimulate,  but  on 
the  contrary  apparently  depress  mitosis.     Their  action  in  this  respect 
also  is  materially  different  from  that  of  heat. 

11.  The  lens  protects  completely  the  retina  of  the  normal  eye  even 
from  the  small  proportion  of  feebly  abiotic  rays  which  can  penetrate 
the  cornea  and  vitreous  humor. 

12.  Experiments  on  rabbits,   monkeys  and  the  human  subject 
prove  that  the  retina  may  be  flooded  for  an  hour  or  more  with  light 
of  extreme  intensity  (not  less  than  50,000  lux),  without  any  sign  of 
permanent  injury.     The  resulting  scotoma  disappears  within  a  few 
hours.     Only  when  the  concentration  of  light  involves  enough  heat 
energy  to  produce  definite  thermic  lesions  is  the  retina  likely  to  be 
injured. 

13.  The  retina  of  the  aphakic  eye,  owing  to  the  specific  and  general 
absorption  of  abiotic  radiations  by  the  cornea  and  the  vitreous  body, 
ij  adequately  protected  from  injury  from  any  exposures  possible  under 
the  ordinary  conditions  of  life,  even  without  the  added  protection  of 
the  glasses  necessary  for  aphakic  patients. 

14.  To  injure  the  cornea,  iris,  or  lens,  by  the  thermic  effects  of 
radiation,  requires  a  concentration  of  energy  obtainable  only  under 
extreme  experimental  conditions. 

15.  Infra-red  rays  have  no  specific  action  on  the  tissues  analogous 
to  that  of  abiotic  rays.     Any  effect  due  to  them  is  simply  a  matter  of 
thermic  action,  and  such  rays  are  in  the  main  absorbed  by  the  media 
of  the  eye  before  reaching  the  retina. 

16.  Actual  experiments  made  on  the  human  eye  show  conclu- 
sively that  no  concentration  of  radiation  on  the  retina  from  any 
artificial  illuminant  is  sufficient  to  produce  injury  thereto  under  any 
practical  conditions. 

17.  Eclipse  blindness,  the  only  thermic  effect  on  the  retina  of 
common  occurrence  clinically,  is  due  to  the  action  of  the  concentrated 
heat  on  the  pigment  epithelium  and  choroid,  this  heat  being  almost 
wholly  due  to  radiations  of  the  visible  spectrum  within  which  the 
maximum  solar  energy  lies. 

18.  The  abiotic  energy  in  the  solar  spectrum  is  a  meagre  remnant 
between  wave  lengths  295  MM  and  305  ju/x,  aggregating  hardly  a  quarter 
of  1%  of  the  total.     At  high  altitudes  and  in  clear  air  it  is  sufficient 
to  produce  slight  abiotic  effects  such  as  are  noted  in  snow  blindness 
and  solar  erythema,  the  former  only  occurring  with  long  exposures 
under  very  favorable  circumstances  and  the  latter  being  in  ordinary 
cases  complicated  by  an  erythema  due  to  heat  alone.     The  amount 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         759 

of  abiotic  energy  required  to  produce  a  specific  effect  in  solar  erythema 
is  substantially  the  same  as  that  required  for  mild  photophthalmia. 

19.  Erythropsia  is  not  in  any  way  connected  with  the  exposure 
of  the  eye  to  ultra  violet  radiations,  but  is  merely  a  special  case  of 
color  fatigue,  temporary  and  without  pathological  significance. 

20.  Vernal  catarrh  and  senile  cataract  we  can  find  no  evidence  for 
considering  as  due  to  radiations  of  any  kind. 

21.  Glass  blower's  cataract  often  charged  to  specific  radiation, 
ultra  violet  or  other,  we  regard  as  certainly  not  due  to  ultra  violet 
light  but  probably  due  to  the  overheating  of  the  eye  as  a  whole 
with  consequent  disturbed  nutrition  of  the  lens. 

22.  Commerical  illuminants  we  find  to  be  entirely  free  of  danger 
under  the  ordinary  conditions  of  their  use.     The  abiotic  radiations, 
furnished  by  even  the  most  powerful  of  them,  are  too  small  in  amount 
to  produce  danger  of  photophthalmia  under  ordinary  working  condi- 
tions even  when  accidentally  used  without  their  globes.     The  glass 
enclosing  globes  used  with  all  practical  commercial  illuminants  are 
amply  sufficient  to  reduce  any  abiotic  radiations  very  far  below  the 
danger  point. 

23.  Under  ordinary  conditions  no  glasses  of  any  kind  are  required 
as  protection  against  abiotic  radiations.     The  chief  usefulness  of 
protective  glasses  lies  not  so  much  in  their  absorption  of  any  specific 
radiations,  as  in  their  reducing  the  total  amount  of  light  to  a  point 
where  it  ceases  to  be  psychologically  disagreeable  or  to  be  incon- 
veniently dazzling.     Glasses  which  cut  off  both  ends  of  the  spectrum 
and  transmit  chiefly  only  rays  of  relatively  high  luminosity,  give  the 
maximum  visibility  with  the  minimum  reception  of  energy.     For 
protection  against  abiotic  action  in  experimentation,  or  in  the  snow 
fields,  ordinary  colored  glasses  are  quite  sufficient. 

24.  So  far  as  direct  destruction  of  bacteria  within  the  cornea  or 
any  other  tissues  of  the  body  is  concerned,  abiotic  radiations  possess 
no  therapeutic  value.     This  is  due  to  the  fact  that  abiotic  radiations 
that  are  able  to  penetrate  the  tissues  are  more  destructive  to  the  latter 
than  to  bacteria. 


SYSTEMATIC  REVIEW  OF  THE  LITERATURE  RELATING 

TO  THE  EFFECTS  OF  RADIANT  ENERGY 

UPON  THE  EYE. 

BY  C.  B.  WALKER,  A.M.,  M.D. 
CHRONOLOGICAL  ACCOUNT. 

Historically  we  find  the  first  study  of  the  properties  of  the  ultra 
violet  light  in  connection  with  the  eye  was  commenced  long  before 
high  power  lamps  were  invented  or  the  r61e  of  ultra  violet  rays  in 
producing  eye-injuries  was  established.  The  first  work,  was  stimu- 
lated by  purely  scientific  interest  with  no  prophylaxis  or  therapy  in 
view;  in  fact  these  latter  factors  did  not  enter  for  several  decades. 

As  early  as  1845,  Brucke 58  laid  the  foundations  for  subsequent  work, 
in  his  investigation  of  the  reason  for  the  invisibility  of  the  ultra  violet 
rays.  In  order  to  determine  whether  these  rays  failed  to  traverse 
the  eye  media  or  failed  to  stimulate  the  retina,  he  first  studied  the 
absorptive  power  of  the  eye  media.  He  found  that  Gum  Guaiacum 
had  a  characteristic  bluish  appearance  in  ultra  violet  light.  By 
means  of  this  substance  he  was  able  to  say  that  the  lens  absorbed 
ultra  violet  rays  strongly  and  the  cornea  and  the  vitreous  humor  to  a 
less  extent.  Later  with  the  assistance  of  Karstein  he  found  with 
sensitive  paper  that  a  combination  of  lens,  vitreous  humor  and 
cornea,  diminished  somewhat  the  intensity  of  the  violet,  began  to 
absorb  more  just  outside  the  visible  spectrum,  was  especially  strong 
on  the  "M"  (372 /*//)  line  of  the  Draper  spectrum,  and  practically 
total  beyond,  that  is  for  rays  less  than  370  up. 

In  1852  Stokes357  discovered  fluorescence  and  thus  afforded  another 
means  of  studying  the  absorption  of  the  eye  media.  Donders 97  with 
Rees  in  1853  threw  a  solar  spectrum  upon  a  screen  covered  with  qui- 
nine sulphate  which  by  its  fluorescence  rendered  the  ultra  violet  rays 
visible.  Various  eye  media,  unfortunately  enclosed  in  glass  con- 
tainers, were  then  interposed  in  the  path  of  the  ultra  violet  rays.  The 
absorption  power  of  glass  itself  rendered  these  results  of  little  value. 

In  1855  Helmholtz 161  studied  the  lower  limit  of  the  visible  spectrum 
using  a  quartz  prism,  but  his  high-grade  myopia  interfered.  He  also 
used  the  fluorescing  screen  of  quinine  sulphate  and  studied  the  fluo- 

760 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         761 

rescence  of  the  crystalline  lens,  of  various  solutions  and  of  the  retina. 
The  fluorescence  of  the  latter  he  discovered  in  the  morbid  state  with 
Setschenow.  A  number  of  observers,  Eisenlohr  106  in  1856,  Janssen  19 
in  1860,  Franz  121  in  1862,  Listing  228  in  1865,  Mascart  24°  in  1869, 
Sekulic  334  in  1872  and  Sauer  305  in  1875  continued  the  study  of  the 
same  question  of  the  length  of  the  visible  spectrum  in  much  the  same 
manner.  Their  results,  with  the  exception  of  those  of  Eisenlohr  and 
Sauer,  added  little  however,  since,  as  the  latter  pointed  out  they 
were  not  free  from  certain  objections  which  will  be  taken  up  more 
in  detail  under  the  discussion  of  the  properties  of  the  lens. 

As  early  as  1858,  Charcot  65  gave  the  first  description  of  photoph- 
thalmia  and  erythema  produced  by  a  small  electric  laboratory  furnace 
(cf.  page  635). 

In  1867  Czerny  85  made  the  first  experimental  observations  on  the 
effect  of  direct  sunlight  on  the  retina.  Even  through  heat  filters 
he  found  he  could  produce  in  the  rabbit's  eye  marked  destruction  of 
retinal  elements  in  10  to  15  seconds  exposure  with  concentrated  sun 
rays.  Deutschman  89  later  (1882)  showed  that  these  changes  could  be 
noted  in  1  second  in  the  same  manner.  Herzog  176  confirmed  these 
results  in  1898  and  reduced  the  exposure  time  to  f  sees.  In  some 
of  these  cases  there  were  cataractous  lens  changes  but  no  outer  eye 
disturbance. 

Tyndafl  37°  in  1876,  made  an  important  contribution  to  the  subject 
in  establishing  the  fact  that  ultraviolet  rays  are  absorbed  by  the 
atmosphere,  since  the  ultra  violet  content  of  the  solar  spectrum  was 
found  to  be  much  greater  on  high  mountains  than  on  low  plains. 

In  1806  418  Wenzel  and  later  von  Beer  in  1817  184  pointed  out  the 
disposition  to  cataract  among  glass  blowers. 

The  introduction  of  the  arc  light  in  1879  and  1880  mark  an  epoch 
in  the  history  of  this  subject,  for  at  least  two  reasons;  first,  because  a 
means  was  afforded  for  far  more  accurate  and  extensive  study  of  ultra 
violet  light  which  the  electric  arc  so  abundantly  supplies;  secondly 
because  immediately  after  the  use  of  the  electric  arc  for  lighting 
and  high  temperature  furnaces  became  general,  cases  of  what  was 
later  designated  as  ophthalmia  electrica,  began  to  make  their  appear- 
ance. Martin  237  and  Nodier  258  in  1881  reported  on  these  cases,  and 
although  they  correctly  described  the  symptom  complex,  their  expla- 
nation of  the  phenomenon  as  a  sympathetic  reflex  from  the  injured 
retina  was  soon  proved  to  be  incorrect. 

In  1882  Leber  221  after  studying  the  cases  of  cataract  formation 
after  exposure  to  lightning  came  to  the  conclusion  that  such  cataracts 
were  produced  electro-chemically. 


762  WALKER. 

In  1883  de  Chardonnet67  used  the  ultra  violet  rays  from  the  arc 
light  to  study  the  absorption  power  of  various  parts  of  the  eye,  and 
emphasized  for  the  first  time  the  very  important  role  of  the  lens 
as  a  determinant  for  the  limit  of  visibility  of  the  short  waves  of  the 
spectrum,  by  virtue  of  having  the  highest  absorption  power  of  all  the 
eye  parts.  He  argued  therefore  that  aphakic  eyes  should  have  a 
greater  range  of  spectral  vision  than  normal  eyes.  Accordingly 
he  examined  two  patients  who  had  clear  eye  media  after  the  extraction 
of  cataractous  lenses.  He  asked  these  patients  to  observe  an  arc  light 
through  a  quartz  glass  plate,  thinly  silvered  so  as  to  cut  out  all  rays 
except  those  between  343  MJ,  and  301  (JL/J,  lines.  Normal  eyes  could  not 
make  out  on  looking  through  this  glass  whether  the  arc  light  was 
burning  or  not,  but  the  aphakic  patients  could  even  detect  motion  of 
the  light. 

In  1886  Meyhof  er  245  found  11.6%  of  glass  blowers  under  40  years  of 
age  had  cataracts,  and  these  were  mostly  left  sided  where  heat  exposure 
was  greatest. 

In  1888  Hess 177  allowed  an  electric  spark  to  impinge  on  the  supra- 
orbital  region  of  a  rabbit  and  produced  equatorial  cataracts.  There 
was  more  or  less  central  distruction  of  lens  capsule  and  vacuolization 
of  anterior  lens  fibres  with  peripheral  increase  of  mitotic  figures  in 
the  capsule.  This  result  was  later  confirmed  by  Chiribuchi,  but  was 
shown  to  be  an  electrochemical  rather  than  abiotic  effect. 

It  remained  for  Widmark  415  in  1889  to  experiment  with  the  effect 
of  ultra  violet  light  on  the  eyes  of  the  laboratory  animals.  He  repro- 
duced the  stages  of  electric  ophthalmia  in  the  rabbits'  eyes  and  con- 
sidered the  reaction  to  be  of  the  nature  of  an  inflammatory  erythema. 
He  first  demonstrated  the  protective  power  of  the  lens  by  interposing 
a  fresh  rabbit's  lens  in  the  path  of  the  ultra  violet  rays  to  which  the 
rabbit's  eye  was  exposed.  The  rabbit's  eye  in  this  case  failed  to  give 
the  characteristic  reaction. 

Hirschberg 172  in  1898  first  suggested  the  possible  influence  of  intense 
sunlight  in  producing  early  senile  cataracts  in  India  and  in  the  country, 
though  Schulek329  had  in  1895  from  the  statistics  of  Grosz,  already 
noted  that  the  senile  cataract  was  more  common  in  people  working 
on  the  hot  plains  than  in  city  dwellers.  Schwitzer332  was  the  first 
to  incriminate  the  ultra  violet  portion  of  the  sunlight  as  an  etiological 
factor  in  these  cases.  Hirschberg184  in  1901  first  noted  that  the 
senile  cataract  almost  always  began  in  the  lower  quadrant  of  the  lens. 
Perhaps  stimulated  by  the  possibilities  of  protection  to  the  eyes  sug- 
gested by  Widmark's  experiments,  Schuleks345  in  1900,  examined  a 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         763 

great  number  of  substances  for  protective  properties.  Unfortunately 
the  substances  he  found  to  have  the  necessary  transparency  and  ab- 
sorptive power  were  certain  liquid  solutions.  His  results  for  the 
absorptive  powrer  of  the  lens  and  the  other  parts  of  the  eye  were  -the 
same  as  those  obtained  by  de  Chardonnet.  The  study  of  protective 
glasses  was  later  taken  up  by  Staerkle348,  and  Vogt396,  and  quite 
recently  with  more  success  by  Hallauer 154*155,  Schanz  and  Stock- 
hausen312,  and  Birch-Hirschfeld31. 

Widmark 318  in  1901  and  1902  continued  to  develop  the  experimental 
method  of  studying  the  problem  on  the  eyes  of  laboratory  animals. 
He  introduced  some  very  ingenious  experimental  arrangements  and 
was  the  first  to  show  with  the  aid  of  the  microscope  that  ultra  violet 
rays  can  produce  definite  pathological  lesions  of  the  corneal  and  lens 
epithelium  as  well  as  of  the  conjunctiva  and  the  skin  of  the  lids  and 
face.  Further  he  believed  he  had  ascertained  that  the  injuries  to  the 
lens  can  be  readily  aggravated  until  cataract  formation  is  the  result. 
He  found  that  heavy  glass  (18  mm.  thick)  when  interposed  prevented 
these  changes.  Solutions  of  quinine  sulphate  were  equally  protective. 
He  was  the  first  to  note  the  similarity  of  ophthalmia  electrica  and  the 
outer  eye  trouble  in  snow-blinding. 

It  was  not  till  1907  that  these  results  received  some  confirmation 
by  Hess 179.  A  number  of  observers  had  looked  for  lens  changes  both 
before  and  afterwards  without  success,  or  with  variable  results.  Thus 
Ogneff 259  in  1896  using  an  arc  light  of  5000  to  8000  c.  p.  noticed  no- 
lens trouble  but  much  outer  eye  trouble  as  Widmark415  had  shown 
in  1889.  Herzog 176  in  1898  repeated  this  work  with  a  heat  filter  and 
a  common  glass  optical  system  on  young  rabbits  and  considered  that 
any  small  effect  such  as  he  found  was  due  to  heat  transformation. 
Birch-Hirschfeld 30  in  1904-5  found  no  lens  changes  with  4-10  min. 
exposure  to  a  4  amp.  Finsen  light.  Hertel350  in  1903  using  the 
magnesium  spark  likewise  noted  no  lens  change;  nor  did  Strebel175 
using  5  min.  exposures  to  a  6  amp.  iron  arc  light. 

Hertel's 175  work  in  1903  was  based  on  his  idea  that  the  pathogenic 
range  of  ultraviolet  rays  should  be  determined  on  the  living  cell 
rather  than  on  the  photographic  plate  since  there  was  a  difference 
in  the  action  of  these  rays  on  chemical  and  living  substance.  He 
therefore  enclosed  certain  bacilli,  in  tiny  quartz  glass  boxes  which 
could  be  inserted  into  the  aqueous  or  vitreous  chambers  of  the  eye. 
Exposing  the  eye,  then,  to  the  ultra  violet  rays  from  a  magnesium 
electrode  spark,  he  found  that  waves  of  280  /JL/J,  would  not  pass  through 
the  lens  and  kill  the  organisms  (B.  Coli)  behind  it  even  after  60  min. 


764  WALKER. 

exposure,  while  bacteria  in  the  anterior  chamber  were  killed  in  25  to 
30  min.  but  not  in  the  control  with  common  glass  interposed  (cf. 
page  749).  In  none  of  the  eyes,  26  in  all,  was  lens  trouble  noted. 

In  1904  definite  pathological  changes  believed  to  be  due  to  ultra 
violet  light  were  noted  by  Birch-Hirschfeld 38  in  the  finer  structures  of 
the  retina. 

In  1906  and  1907  Vogt395  and  Hallauer 153  began  the  careful  study 
of  transparent  and  colorless  protection-glasses,  and  the  latter  produced 
by  a  secret  process  the  so  called  "  Hallauer  glass." 

In  1907  Schanz  and  Stockhausen 309  also  invented  and  patented  a 
new  glass,  which  they  called  "  Euphos  glas." 

In  1908  Birch-Hirschfeld 35  studied  in  five  cases  visual  field  changes 
produced  by  uviol  lamps,  showing  sector  and  ring  formed  scotomata 
for  red  and  green  to  be  the  predominant  varieties,  but  later  (1912) 
he  objected  41  to  the  ringscotoma  found  by  Jess  20°  in  the  same  year. 

Voege  388  in  1908  asserted  that  daylight  might  be  taken  as  the  ideal 
light,  especially  "cloud  light."  He  compared  the  spectra  of  various 
high  power  lights  protected  with  milk  and  opal  glass  coverings,  with 
the  spectra  of  cloud  light  and  found  them  to  compare  favorably,  and 
therefore  concluded  that  these  lights  so  protected  are  not  to  be  con- 
sidered dangerous  when  properly  used. 

In  1909  Schanz  and  Stockhausen316  vigorously  opposed  this  attitude 
and  their  view  was  supported  in  the  same  year,  by  the  appearance  of 
the  statistical  study  of  Handmann 157  showing  that  the  senile  cataract 
begins  in  the  region  of  the  lens  most  exposed  to  the  short  wave  length 
light  of  the  sky,  that  is  in  the  lower  half. 

In  this  year  Birch-Hirschfeld38,  Schanz  and  Stockhausen316,  and 
Hallauer152  (on  human  lens  only),  by  spectrophotographic  method, 
measured  with  the  greatest  care,  the  absorptive  power  of  various  kinds 
of  glass,  the  cornea,  vitreous  humor  and  lens  of  various  animals  and  of 
the  human  eye.  They  also  made  careful  measurements  of  the  spectral 
range  of  a  great  variety  of  light  sources  with  and  without  covering 
of  common  glass,  milk  glass  and  opal  glass. 

In  1910  Schanz  and  Stockhausen  318  made  a  very  careful  study  of  the 
fluorescence  of  the  human  lens  by  a  hitherto  unused  method,  and  also 
examined  more  carefully  than  before  the  spectrum  of  the  glass  blowers' 
furnace  and  the  conditions  under  which  the  glass  blowers  were  forced 
to  work.  They  contended  that  the  glass  makers'  cataract  is  due  the 
longer  of  the  ultra  violet  rays  with  perhaps  the  assistance  of  the  short- 
est visible  rays. 

Also  in  1910  Hertel  and  Henker 172  accepting  Voege's  idea  that  the 


EFFECTS   OF   RADIANT   ENERGY  ON  THE   EYE.  765 

ideal  light  is  cloud  light  or  skylight,  used  the  most  accurate  instruments 
available  in  the  laboratory  of  C.  Zeiss,  in  Jena,  to  measure  the  percent- 
age absorptive  power  at  different  points  in  the  spectrum,  of  various 
glasses.  These  glasses  were  all  found  to  be  inferior  to  opal  and  milk 
glass  for  the  purpose  of  enclosing  strong  arc  lights  to  produce  a  spec- 
trum most  nearly  approaching  in  quality  and  quantity,  the  spectrum 
obtained  from  sky  light. 

Recently  (1912)  Martin 238  has  verified  some  of  the  results  of 
\Vidmark,  Hess,  and  Romer,  while  Carl  Behr 17  has  reported  some 
very  interesting  functional  disturbances  of  light  adaption  power  of 
the  eyes  in  patients  working  by  artificial  light.  These  results  will 
later  be  taken  up  more  in  detail. 

Having  thus  rapidly  traced  the  important  steps  in  the  progressive 
development  of  the  knowledge  of  ultra  violet  light  in  relation  to  the 
eye,  the  mass  of  findings  may  doubtless  be  rendered  much  more 
available  by  considering  them  separately  and  in  more  detail  with, 
reference  to  the  various  parts  of  the  eye. 


THE    OUTER    EYE. —  PHOTOPHTHALMIA,  VERNAL  CATARRH. 

Probably  ophthalmologists  have  experienced  less  difficulty  in  reach- 
ing definite  conclusions,  concerning  the  condition  called  ophthalmia 
electrica  or  photophthalmia  (Parsons265),  than  with  any  of  the  other 
effects  of  ultra  violet  light.  As  to  the  symptom  complex  little  has 
been  added  since  the  first  report  in  1858  (cf .  page  635)  of  Charcot 65 
and  the  later  observations  of  Martin  238  and  Nodier  258  in  1881,  shortly 
after  the  general  introduction  of  the  electric  arc  for  lighting  and 
furnaces,  (in  1879  and  1880).  The  workmen  most  exposed  to  these 
arcs,  particularly  the  furnace  arc,  began  to  complain  of  symptoms 
that  we  now  know  to  be  due  to  photophthalmia  (see  page  634). 
In  a  week  the  eyes  were  practically  normal.  The  affection  of  the  sur- 
rounding skin  known  as  dermatitis  electrica  was  not  unlike  that  of 
sunburning  of  severe  grade  except  in  its  origin.  As  in  sunburn,  a 
tanning  was  notable  after  the  inflammation  had  subsided,  for  several 
weeks.  Although  retinal  changes  were  seldom  noted  with  the  oph- 
thalmoscope, functional  disturbances  were  observed  such  as  temporary 
blindness  or  scotomata,  floating  spots  of  red,  yellow  or  blue  or  occasion- 
ally erythropsia,  or  red  vision.  Therefore  the  very  early  writers  were 
inclined  to  believe  the  outer  eye  trouble  followed  sympathetically 
from  the  retinal  injury.  These  retinal  disturbances  also  led  Terrier 363 


766  WALKER. 

in  1888  to  divide  the  large  number  of  reported  cases  into  two  classes; 
a  mild  group  without  retinal  disturbances  and  of  good  prognosis, 
and  a  severe  group  with  retinal  disturbances  and  of  bad  prognosis. 
However,  after  the  classical  experiments  of  Widmark  these  theories 
and  classifications  were  no  longer  found  to  be  useful.  Widmark41 
in  1889  exposed  the  rabbit's  eye  to  various  parts  of  the  arc  light  spec- 
trum. He  found  that  when  a  1200  c.  p.  arc  light  was  used  for  10 
min.  on  the  rabbit's  eye  without  screening  out  any  ultra  violet  rays 
all  the  typical  symptoms  of  electric  ophthalmia  appeared  after  a 
latent  period  of  6  hours.  By  varying  the  time  of  exposure  any  degree 
of  injury  could  be  produced  from  a  mild  erythema  to  ulceration  of  the 
conjunctiva  and  cornea.  But  if  a  common  glass  plate  0.5  to  1.0  cm. 
thick  was  interposed  the  rabbit  was  entirely  protected.  Thus  he 
established  for  the  first  time  that  rays  below  SOOyuju  in  length  were 
chiefly  responsible  for  the  outer  eye  trouble.  This  particular  point 
was  confirmed  by  Ogneff  259,  Hess  m,  Kiribuchi 203  and  subsequently 
by  practically  all  observers.  Further  Widmark  concluded  that  ultra 
red  and  the  visible  rays  are  entirely  without  effect,  outside  of  common 
heating  effects. 

Widmark  made  another  important  contribution  to  the  knowledge 
of  this  subject  when  he  drew  attention  to  the  striking  resemblance 
of  ophthalmia  electrica  and  the  disturbance  found  on  the  outer  eye 
in  cases  of  snow-blinding.  He  showed  that  they  both  had  the  same 
latent  period  and  were  ushered  in  with  the  same  syndrome  of  symp- 
toms. Further  that  erythropsia,  temporary  blindness,  or  blind  spots 
occurred  in  both.  The  fact  that  ultra  violet  light  is  stronger  on  high 
mountains  and  snow  covered  surfaces  as  had  been  shown  by  Tyndall 
and  subsequently  verified  by  Helmholtz,  Langley,  Cornu  and  Mascart, 
was  a  further  argument  emphasized  by  Widmark  in  support  of  his 
contention  that  ultra  violet  rays  are  responsible  for  both  ophthalmia 
electrica  and  snow  blinding. 

Birch-Hirschfeld,  Hertel,  Best  and  others  had  up  to  1907  found  a 
thick  plate  of  common  glass  to  be  sufficient  protection  from  electric 
ophthalmia  as  Widmark  had  pointed  out.  But  in  1907  Stockhausen 
after  one  half  hour  working  with  arc  lights  received  a  severe  ophthal- 
mia electrica  through  glass  protection.  Schanz  &  Stockhausen310 
therefore  repeated  Widmark's  experiment  and  found  common  glass 
to  be  inefficient  protection  for  long  intense  exposure.  They  were 
able  to  produce  the  characteristic  symptom  in  a  rabbit's  eye  through 
18  mm.  of  common  glass  after  4  hours'  exposure  to  a  15  amp.  arc  light. 
Thus  stimulated  they  studied  the  manufacture  of  glass  carefully, 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         767 

and  finally  produced  the  yellowish  colored  "Euphos  glas"  which 
they  recommend  as  very  satisfactory,  not  only  for  protection  glasses, 
but  also  for  use  in  making  arc  light  coverings  or  mantles. 

However  Birch-Hirschfeld  34  in  1907  considered  the  above  exposure 
so  intense  as  to  afford  no  criterion  for  cases  as  they  usually  occur. 
From  his  results  he  asserted  that  one  need  not  be  afraid  to  use  the 
ordinary  smoked,  uviol,  flint,  or  even  common  glass,  in  the  great 
majority  of  cases.  He  exposed  a  rabbit's  eye  for  1  hour  as  close  as 
10  cm.  to  a  uviol  lamp  (mercury  vapor  tube)  protected  only  by  a  2  mm. 
thickness  of  common  glass.  After  the  6  hour  latent  period  no  symp- 
toms whatever  developed  although  the  control  rabbit's  eyes  were 
badly  damaged.  Further  he  exposed  his  own  eyes  to  a  3000  c.  p. 
quartz  mercury  arc  lamp  at  1  meter  distance  using  smoked  glass 
goggles  as  a  protection.  Although  the  surrounding  skin  of  his  face 
was  burned,  no  symptoms  of  ophthalmia  electrica  developed.  Birch- 
Hirschfeld  34  also  proved  that  by  daily  exposure  of  the  rabbit's  eye  to 
ultra  violet  rays  a  chronic  inflammation  of  the  outer  eye  could  be 
produced  which  was  very  similar  in  appearance,  both  grossly  and  his- 
tologically,  with  vernal  catarrh,  originally  considered  by  Schiele 233 
in  1899  to  be  a  result  of  exposure  to  the  light  rays  of  the  sun.  In  this 
investigation  Birch-Hirschfeld  exposed  the  rabbit's  eyes  for  10  min. 
every  day  for  180  days  at  a  distance  of  10  cm.  from  the  "  Uviol  lampe" 
of  Schott.  The  eye  lids  of  the  rabbits  were  everted  during  the  expo- 
sure. After  passing  through  the  usual  acute  ophthalmia  electrica  a 
chronic  inflammation  was  established  similar  to  vernal  catarrh, 
but  no  trouble  in  the  lens  or  retina  was  noted. 

Birch-Hirschfeld  considered  rays  shorter  than  330  H/JL  to  be  prima- 
rily responsible  for  the  outer  eye  disturbance  in  this  case,  still  rays  from 
330  fjLfj,  to  400  /jifj.  or  more  could  not  be  excluded  as  etiological  factors. 
However  he  agreed  with  Axenfeld  and  Ruprecht 9,  1907,  that  these 
factors  could  not  entirely  explain  vernal  catarrh.  Vogt401  in  1912 
thought  that  exacerbations  at  least  in  the  disease  depended  on  thermic 
influences. 

THE  CORNEA:  —  ABSORPTION,  INJURIES. 

That  the  cornea  might  suffer  severe  injury  in  bad  cases  of  oph- 
thalmia electrica  was  early  noted  by  Terrier363  in  his  report  of  1888. 
In  these  cases  a  dull  haziness  of  the  cornea  with  perhaps  a  phylectenu- 
lar  condition  or  bleb  formation  was  first  noted.  This  condition  could 
either  go  on  to  ulcer  formation  by  infection  or  to  panuus  formation 


768  WALKER. 


by  vascularization.  The  ulcer  formation  as  is  usually  the  case,  often 
ead  to,  or  was  accompanied  by,  iritis.  Corneal  disturbance  in  snow 
blinding  has  been  occasionally  reported.  Hildige191  in  1861  and 
Reich 184  in  1880  saw  small  ulcers. 

Widmark  415  in  1889  studied  the  progress  of  the  earliest  changes  on 
the  cornea  due  to  ultra  •  violet  rays.  With  the  aid  of  the  microscope 
he  found  first  in  the  corneal  epithelium  a  swelling  and  necrosis  of  the 
nuclei  leading  to  necrosis  of  epithelial  cells,  and  small  areas  of  desqua- 
/  mation  followed  sometimes  by  ulcerative  conditions  and  usually  by 
opacities.  These  findings  were  at  once  verified  by  Ogneff259  and 
Bresse 59  and  later  by  many  others.  Hertel  Xr7  in  1903,  repeating  this 
experiment  and  with  rays  of  309  n/j,  to  280  n/j,  from  the  magnesium 
spark,  was  able  to  produce  the  same  corneal  injuries,  as  well  as  to  kill, 
or  at  least  demoralize  bacilli  enclosed  in  quartz  containers  and  placed 
in  the  anterior  chamber.  This  could  not  be  done  when  common  glass 
was  interposed  in  the  control  experiment.  That  this  fact  may  be 
taken  as  evidence  that  rays  of  280  juyu  were  able  to  penetrate  the  cornea 
does  not  follow,  was  pointed  out  two  or  three  years  later  by  Birch- 
Hirschfeld,  Schanz  and  Stockhausen,  who  considered  that  rays  of 
greater  length  than  280  ju/z  in  sufficient  amount  to  kill  organisms 
could  not  be  excluded  (cf.  page). 

Widmark  made  no  attempt  to  determine  the  absorptive  power  of 
the  cornea  by  spectrophotographic  methods.  Schanz  and  Stock- 
hausen312 were  among  the  first  to  attempt  accurate  measurements 
in  this  way  on  the  human  as  well  as  on  the  animal  cornea.  They 
found  that  all  rays  below  300  (JL/JL  are  absorbed  by  the  cornea.  Hess, 
Birch-Hirschfeld  and  Herzog  verified  this  measurement  and  again 
later  Birch-Hirschfeld32  attempting  still  greater  accuracy,  with  the 
same  method,  placed  the  absorptive  limit  at  306  /ijii.  Parsons 266  in 
England  in  the  same  way  found  rays  above  295  w  able  to  penetrate 
the  cornea. 

Still  later,  in  1909  Schanz  and  Stockhausen  reconsidered  the  limit 
of  300  /JL/J,  for  the  absorptive  power  of  the  cornea  placing  it  at  320  MM 
for  all  practical  purposes,  since  the  spectrum  was  so  weakened  be- 
tween 320  nn  and  300  juju  as  to  be  without  action  on  the  lens.  300  ju/i 
was  however  still  considered  the  point  of  complete  absorption. 

Martin238  in  1912  agreed  with  Parsons  that  the  cornea  offered  no 
resistance  to  waves  above  295  jitju  length  but  all  beyond  this  limit  were 
completely  cut  off. 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          769 


THE  AQUEOUS  AND  VITREOUS  HUMORS. 

The  humors  of  the  eye  seem  to  be  the  most  silent  regions  as  far  as 
response  to  insult  from  ultra  violet  light  sources  is  concerned.  Since 
they  have  an  absorptive  power,  never  greater,  and  often  less  than  that 
of  the  cornea,  the  latter  apparently  protects  them  from  the  action  of 
the  injurious  rays. 

Bonders97  who  made  the  first  attempt  to  measure  the  absorptive 
power  of  vitreous  humor  alone  was  not  aware  of  the  fact  that  the 
containing  vessel  must  be  made  of  thin  quartz  glass,  so  that  his  re- 
sults were  of  no  value.  After  him  Soret 345  in  1879  reported  the  first 
reliable  results.  He  found  the  vitreous  humor  able  to  absorb  rays 
of  lengths  less  than  294.8  nfj,  in  thicknesses  of  1  cm.  and  still  smaller 
values  for  thinner  layers.  The  values  of  de  Chardonet 67  in  1883 
were  still  lower.  He  found  the  absorptive  value  to  lie  between  the 
310  MM  and  304  IJL/JL  lines. 

Birch-Hirschfeld 34  in  1909  found  that  the  vitreous  humor  in  1  cm. 
layers  has  an  absorptive  power,  practically  constant  for  all  animals, 
of  rays  less  than  300  /JL/JL  thus  being  the  same  as  common  glass.     Schanz 
and  Stockhausen309,  Vogt396,  Hess178,  Ogneff 259,  Birch-Hirschfeld3^ 
and  all  recent  observers  have  also  confirmed  this  value  for  1  cm.  layers^ j 
of  vitreous  humor.     Parsons  266  for  thinner  layers,  —  ^  of  an  inch, —       | 

found  absorption  to  begin  at  280  w  and  become  complete  at  270  juju,. 

Martin238  in  1912  confirmed  the  later  results  and  found  no  change  in 
the  absorptive  power  of  eye  media  as  long  as  8  hours  after  death. 


THE  IRIS. 

The  iris  and  uveal  tr,act  have  long  been  noted  to  suffer  in 
exposures  to  short  wave  lengths.     Martin  238  and  Nodier  258  in  1881 
noted  inflammation  of  the  iris  in  severe  cases,  confirmed  by  Terrier36 
in  1888.     The  very  short  exposure  with  light  rays  by  Czerny  85  in  1867, 
Deutschman89  in  1898  and  Herzog  176  in  1898  gave  no  notable  iris 
changes  beyond  slight  hyperaemia.     Hess 177  in  1888  by  use  of  the 
electric  spark  impinging  in  the  supraorbital  region,  and  Kiribuchi 203 
in  1900  with  the  Ley  den  jar  spark  were  both  able  to  produce  marked 
uveitis.     Gardner 184  in  1871,  Berlin 22  1888,  and  Ewald  m  1891,  have" 
reported  hyperemic  and  swollen  iris  in  snow  blinding. 

Widmark415   in   1889  noted  microscopically  in  cases  of  2-4  hours 


770  WALKER. 

exposure  a  marked  swelling  and  hyperemia  of  the  ciliary  body,  and  in 
later  experiments  in  the  same  way  noted  small  hemorrhages  in  the 
iris.  Gross  examination  showed  myosis  and  discoloration  of  the  iris. 
Ogneff 259,  Terrier363  and  Weiss31  confirmed  these  findings. 

Birch-Hirschfeld  37  in  1904  with  the  Finsen  3.5  to  4.5  amp.  arc  light 
for  5-10  minutes  noted  iritis  and  cyclitis  in  6-12  hours  with  fibrinous 
exudate  into  the  anterior  and  posterior  chambers.  Further  experi- 
ments in  1908  with  the  Schott  lamp  10  min.  exposures  at  10  cm.  daily 
for  180  days  showed  practically  no  effect  on  the  iris  though  a  chronic 
conjunctival  inflammation  was  produced. 

Martin238  in  1912  noted,  in  rabbits  exposed  1|  to  2  hours  at  a  dis- 
tance of  1  in.  from  a  Kromayer  mercury  vapor  lamp  hyperemia  and 
myosis  of  the  iris  but  no  exudates.  Further  by  the  hemolytic  method 
of  Romer  he  found  that  the  iris  showed  evidence  of  damage  with  inten- 
sities above  1  hour  exposure  at  4  in.  distance.  Whether  the  injury  to 
the  iris  produced  when  the  light  is  of  sufficient  strength  is  a  direct 
result  of  light  rays  or  a  secondary  effect  of  the  corneal  and  outer  eye 
injury  was  not  made  clear. 


THE   LENS:  —  ABSORPTION;    FLUORESCENCE,   AS   A   DETERMINANT 
OF  VISIBILITY  OF  ULTRA  VIOLET  RAYS;   INJURIES;   CATARACTS. 

The  reports  of  different  observers  upon  the  absorption  power  of 
the  crystalline  lens  have  varied  considerably.  Birch-Hirschfeld 37 
in  1909  accounted  for  the  long  list  of  previous  variations  in  the  following 
manner.  Aside  from  the  personal  equation  or  individual  variation 
in  observation,  there  is  a  considerable  variation  in  the  absorptive 
power  of  lenses  of  different  animals  of  the  same  species  as  well  as  of 
different  species.  His  results  may  be  tabulated  thus: 

Range  of 

Average  Variation  in 

Animal  absorption         Different  Animals 

Swine  330  MM  15  MM 

Calf  328  MM  12  MM 

Ox  385  MM  30  MM  increasing  with  age. 

To  a  less  extent  thickness  plays  a  part,  though  not  so  very  great, 
since  5  mm.  of  rabbit  lens  has  about  the  same  absorptive  power  as 
10  mm.  of  ox  lens,  for  waves  less  than  390  MM-  The  formula  for  the 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         771 

effect  of  thickness  or  intensity  before  and  after  transit  shows  a  varia- 
tion possibility  of  small  degree  thus, — 

J1  =  Jo%ekd        where  Ji  =  intensity  after  transit 

Jo  =  intensity  before  transit 
d  =  thickness  and  k  =  coefficient  constant. 

The  human  lens  he  found  to  vary  considerably,  as  will  be  shown  later, 
with  such  factors  as  age,  consistency  and  color. 

As  has  been  stated  the  absorptive  power  of  the  lens  and  other  eye 
media  for  ultra  violet  rays,  and  the  limit  of  visibility  of  the  spectrum  in 
the  ultra  violet  region  are  two  problems  whose  investigation  has  been 
carried  forward  in  the  same  stages  since  it  was  obvious  from  the  start 
that  the  determination  of  one  would  throw  much  light  on  the  other. 

Brucke 58  really  opened  the  subject  in  1845  when  he  speculated  as 
to  the  range  of  the  visible  spectrum  and  the  reason  for  the  invisibility 
of  the  ultra  violet  rays.  In  the  manner  described  he  found  the  ox 
lens  to  absorb  rays  below  370  MM-  Bonders97,  using  the  method  of 
fluorescing  screens  of  quinine  sulphate,  discovered  by  Stokes,  at- 
tempted to  measure  the  absorptive  power  of  the  lens  but  the  glass 
containers  vitiated  his  results. 

Stokes357  by  direct  observation  of  the  solar  spectrum  through  a 
quartz  prism,  thought  he  could  see  as  low  as  the  372  MM>  358  /J./JL, 
and  335  MM  lines  and  perhaps  further. 

In  the  same  way  Helmholtz  161  with  a  quartz  optical  system  could 
see  a  few  lines  in  the  372  MM  and  318  MM  region,  although  his  eyes  were 
very  myopic.  He  also  observed  the  ultra  violet  rays  directly  through 
holes  in  the  fluorescing  region  of  a  screen  of  quinine  sulphate  upon 
which  the  spectrum  was  thrown. 

By  similar  methods  Listing228  placed  the  limit  of  visibility  at  the 
372  MM  line  and  Sekulic  334  at  the  358  MM  line.  Mascart  24°  however, 
using  high  intensity  of  ultra  violet  illumination,  considered  lines  as 
low  as  313  MM  to  be  visible.  Soret 345  by  photographic  methods  found 
the  vitreous  humor  of  the  ox  in  1  cm.  thicknesses  to  have  the  same 
absorptive  power  as  the  cornea  of  294.8  MM-  He  found  that  the  lens 
of  the  ox  absorbs  rays  shorter  than  383  MM.  and  the  entire  eye  has  the 
same  limit.  Nevertheless  he  maintained  that  the  human  eye  could 
see  rays  as  short  as  294.8  MM- 

Eisenlohr 106  threw  doubt  on  these  results  when  he  pointed  out  that 
fluorescence  alters  the  ultra  violet  rays  so  that  the  observation  by 
means  of  or  in  the  presence  of  fluorescent  light,  is  not  accurate.  He 
found  even  on  white  paper  screens  that  fluorescence  rendered  rays 


772  WALKER. 

visible  as  low  as  354  MM  in  length  while  observation  of  the  same  light 
through  the  spectroscope  showed  no  rays  visible  less  than  395.6  MM  in 
length.  Later  Sauer 305  using  metal  electrodes  came  to  the  same  con- 
clusion. 

With  the  use  of  the  arc  light  de  Chardonnet 67  photographed  the  rays 
able  to  pass  through  the  human  lens  and  found  absorption  began  at 
the  "H"  line  (397  MM)  increased  to  the  "L"  line  (381  MM)  and  became 
total  at  the  "M"  line  (372  MM)-  The  absorptive  power  of  the  cornea 
lay  between  the  304  MM  and  299  MM  lines  and  for  the  vitreous  humor 
between  304  MM  and  310  MM-  To  de  Chardonnet  belongs  the  credit  of 
properly  emphasizing  the  significance  of  the  higher  absorption  of  the 
lens  in  determining  the  lower  limit  of  visibility  of  the  spectrum.  He 
concluded  that  patients  having  clear  media  after  cataract  operations 
could  see  more  of  the  spectrum  than  normal  eyes.  By  thinly  silvering 
a  quartz  glass  plate  he  was  able  to  prevent  all  except  rays  below  the 
343  MM  line  from  passing  through  so  that  when  normal  eyes  attempted 
to  observe  an  arc  light  through  the  plate  it  was  entirely  invisible.  He 
found  two  aphakic  patients  however  who  could  tell  when  the  arc 
light  was  turned  on  and  off  or  when  it  was  moved  while  lighted. 

Widmark416  next  took  up  this  question  in  a  very  thorough  manner. 
He  used  Hasselberg's  modification  of  Rowland's  spectroscope  using  a 
grating  with  a  radius  of  1.6  meters.  The  light  source  was  an  arc  light 
with  iron  poles.  The  discontinuous  spectrum  obtained  in  this  way 
gives  sharp  well  known  lines  to  examine  and  is  free  from  aberrant  light. 
Widmark  examined  eight  aphakic  patients  ranging  from  59  to  68  years 
of  age.  Seven  could  see  lower  in  the  scale  than  he,  himself,  could. 
Four  of  these  were  examined  roughly  by  observing  the  spectrum 
thrown  on  a  screen.  One  of  these  could  see  no  better  than  himself 
so  that  the  above  more  accurate  method  was  used  on  the  second  four 
giving  the  following  results  for  the  ultra  violet  limit, —  313  MM>  313  MM> 
342  MM  and  344.5  MM- 

In  order  to  test  the  normal  range  at  various  ages  for  comparison 
he  examined  59  individuals  ranging  from  11  yrs.  to  74  yrs.  of  age. 

The  results  are  here  tabulated. 


No.  of  Individuals 

Age  in  years 

Lower  limit  of  vision  in  fJ-fJ- 

10 

11-20 

378-395     Average  =  386 

14 

20-30 

371-395         "         =382.5 

6 

30-40 

372-393         "         =388.9 

13 

40-50 

380-394.5      "         =388.7 

3 

50-60 

378-402         "         =  391  .  7 

10 

62-74 

379-410.8      "         =401.8 

EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         773 

After  55  years  of  age,  only  one  out  of  12  individuals  could  see  rays 
below  395  /JL/JL,  that  is,  in  the  ultra  violet  region.  The  only  medium 
which  changes  at  that  age  is  the  lens,  so  that  it  is  still  more  definitely 
proven  that  the  lens  establishes  the  lower  limit  of  spectral  vision  in 
the  human  eye. 

Birch-Hirschfeld 35  compared  the  visual  threshold  or  distinguishing 
power,  for  various  intensities  of  the  same  wave  length,  in  the  ultra 
violet  region,  of  the  aphakic  eye  and  the  eyes  of  individuals  ranging 
from  14  to  70  years  of  age.  He  was  thus  determining  not  the  ultra 
violet  limit  of  vision,  but  the  intensity  at  which  a  definite  wave  length 
which  both  groups  of  eyes  could  see,  would  become  visible.  He  found 
that  the  threshold  of  the  lensless  eye  exceeded  that  of  the  normal,  eye 
not  inconsiderably,  except  in  the  case  of  a  red  blind  physician  who  had 
developed  a  power  of  distinguishing  small  intensity  changes  that 
almost  equalled  that  for  the  lensless  eye.  As  the  wave  lengths  of  the 
light  used  were  diminished,  he  found  that  the  lensless  eye  gradually 
gained  more  advantage  until  near  381  H/JL  and  below  it  showed  far 
greater  sensitiveness  than  the  normal  eye.  His  results  thus  agreed 
with  those  of  Widmark,  though  the  same  accuracy  was  not  attempted, 
—  (the  screen  method  was  used)  since  his  point  was  only  to  show  the 
relatively  greater  sensitiveness  of  the  lensless  eye,  in  the  short  wave 
than  in  the  long  wave  length  ultra  violet  regions  of  the  spectrum. 

The  appearance  of  the  ultra  violet  spectrum  has  been  variously 
described.  Helmholtz  characterized  it  as  deep  indigo  blue  under 
weak  illumination  to  silvery  blue  under  stronger  illumination.  Seku- 
lic  334  and  Sauer 305  called  it  silver  gray  in  color.  Widmark's  aphakic 
patients  described  the  first  part,  340  MM  to  370  /zju,  as  blue  or  violet  and 
below  that  all  described  it  as  a  weak  light  gray.  More  recently 
Schanz  and  Stockhausen 318,  Birch-Hirschfeld31,  and  others  agree 
on  lavender-gray  as  the  best  descriptive  term. 

The  question  as  to  how  this  sensation  is  produced,  whether  by  direct 
stimulation  of  the  retina  or  by  the  intermediation  of  the  phenomenon 
of  fluorescence  of  the  lens  or  retina,  has  been  variously  answered. 
Soret 343  favored  the  latter  view,  but  the  work  of  Widmark 416  and 
others  shows  that  when  the  lens,  which  fluoresces  more  than  any  other 
part  of  the  eye,  is  removed,  still  greater  range  of  vision  in  the  ultra 
violet  region  is  obtained.  Further  as  pointed  out  by  Widmark41 
and  Mascart240  the  ultra  violet  region  appears  in  sharp  lines  and 
bundles,  not  as  a  blur  of  light  impossible  to  focus  such  as  would  come 
from  the  fluorescing  lens.  Nor  could  the  fluorescence  of  the  retina 
make  these  rays  visible  and  still  give  a  sharp  image.  Thus  according 


774  WALKER. 

to  Tigerstedt366  it  is  generally  accepted  that  the  retina  is  sensitive 
to  such  ultra  violet  rays,  as  are  able  to  penetrate  the  eye  media  and 
be  focussed  upon  it. 

The  same  does  not  hold  for  ultra  red  rays  although  Helmholtz 
thought  it  did  from  the  work  of  Briiche  and  Knoblauch59  in  1846 
who  found  that  heat  from  the  Argand  burner  did  not  penetrate  the  eye 
appreciably.  Cima  73,  1852,  also  Janssen 198,  and  Franz 121  in  1862, 
found  only  about  9%  of  the  heat  from  a  Locatelli  lamp  was  trans- 
mitted. This  was  confirmed  by  Klug  204  in  1878  with  gas  and  sunlight. 
Tyndall 371,  1865,  with  a  650  c.  p.  arc  lamp  found  that  about  3  of  the 
dark  heat  rays  were  transmitted  through  the  vitreous  of  the  ox. 
Engelman110  in  1882  using  the  bacterium  photometricum, —  which 
always  migrates  to  the  infra  red  region  when  exposed  to  the  spectrum, 
as  an  indicator,  found  the  same  phenomena  when  water  glass  vitreous 
lens  or  cornea  was  interposed.  Hertel173  in  1911  showed  the  lower 
limit  of  subjective  and  of  objective  stimulation  of  the  retina  were 
about  the  same,  lying  between  820  ^M  and  840  /JL/JL.  Vogt 401  however, 
in  1912  showed  conclusively  that  a  great  amount  of  the  ultra  red  light 
reaching  the  retina  is  not  visible,  in  fact  as  much  as  80%  or  more. 
Further  on  normal  human  eyes  he  found  that  3%  of  the  heat  reached 
the  retina  and  less  than  1%  passed  on  into  the  orbit.  20%  to  25% 
passed  through  cornea  or  sclerotic.  The  aqueous  absorbed  20-30  % 
of  the  heat  transmitted  by  the  cornea.  The  cornea  iris  and  lens 
together  transmit  6%  of  the  heat  falling  on  the  cornea.  The  lens 
absorbs  30%  of  the  heat  transmitted  by  the  cornea  and  iris.  Vitreous 
absorbs  nearly  60%  of  the  heat  falling  on  its  anterior  surface.  The 
upper  lid  transmits  6%. 

Fluorescence  has  long  been  a  subject  of  much  interest  and  study. 
A.  von  Graefe  knew  that  fluorescence  of  the  lens  was  due  to  ultra 
violet  light  and  Helmholtz  16°  after  an  extended  study  of  the  fluores- 
cence of  the  lens,  quinine  sulphate  solutions  and  other  fluorescing 
bodies,  concluded  that  fluorescence  in  general  is  due  to  the  appearance 
of  rays  of  various  length,  and  is  therefore  really  mixed  or  white  light. 
Fluorescence  was  then  the  result  of  a  transformation  of  ultra  violet 
rays  to  rays  of  greater  wave  length.  He  considered  the  rays  between 
400  nn  and  300  MM>  to  be  chiefly  the  ones  transformed.  Widmark 
noted  an  apparent  decrease  of  fluorescing  power  of  the  lens  as  the  age 
of  the  individual  increased  and  the  absorptive  power  increased. 

Schanz  and  Stockhausen 315  in  1909  took  up  the  question  of  fluo- 
rescence in  connection  with  their  study  of  the  properties  of  "  Eupnos- 
glas"  which  they  found  in  certain  grades  to  absorb  rays  below  400  M/* 


t  EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         775 

and  still  cut  down  the  visible  spectrum  but  little  —  5%  for  a  thickness 
of  10  mm.  They  found  that  fluorescence  of  the  rabbit's  lens  was  not 
diminished  by  18  mm.  of  plate  glass,  therefore  rays  less  than  300  MM 
could  not  be  held  responsible  for  the  fluorescence.  Nor  did  flint  glass 
absorbing  to  350  MM  decrease  the  phenomenon  but  when  Euphos  glas 
was  interposed  the  fluorescence  was  stopped.  Therefore  they  limited 
the  range  of  fluorescing  rays  to  350  MM  to  400  MM-  If  they  allowed  the 
light  to  traverse  both  a  blue  uviol  glass  and  a  Euphos  glas  before 
striking  the  rabbit's  eye  there  was  no  fluorescence  of  the  lens.  Now 
when  the  Euphos  glas  only  was  removed  after  adaptation  had  taken 
place,  much  lid-spasm  and  blinking  of  the  rabbit's  eyes  took  place  as 
the  fluorescence  began.  They  laid  great  stress  on  this  occurrence  as 
an  indication  of  the  painful  and  injurious  effect  of  this  group  of  rays, 
350  MM  to  400  MM>  on  the  retina.  From  a  study  of  the  spectrum  in 
this  region  photographed  through  the  whole  eye  media  and  from  the 
appearance  of  the  fluorescence  itself,  they  came  at  this  time  to  the 
conclusion  that  fluorescence  was  due  not  as  Helmholtz  said  to  trans- 
formation of  short  wave  ultra  violet  light  to  longer  waves  of  different 
length  in  the  visible  field,  but  due  to  the  appearance  of  a  new  spectral 
color  lavender-gray  of  definite  wave  length.  Not  only  did  they  con- 
sider fluorescence,  as  did  Widmark,  to  decrease  with  age  but  also  with 
length  of  time  of  exposure,  since  the  fresh  lens  from  a  gliomic  eye 
of  a  child  diminished  notably  in  fluorescing  power  after  exposure  of  a 
few  hours.  This  decrease  of  fluorescing  power  they  attributed  to 
some  breaking  down  or  change  in  chemical  composition  which  they 
supposed,  without  analytical  proof,  to  be  involved  in  the  production 
of  fluorescence. 

Birch-Hirschfeld 38  at  once  objected  to  these  conclusions,  consider- 
ing that  nothing  had  been  offered  as  real  proof  against  the  Helmholtz 
theory  of  fluorescence.  He  maintained  that  nothing  had  been  shown 
as  to  the  nature  of  fluorescence  and  even  questioned  whether  the 
range  of  rays  responsible  could  be  established  in  the  manner  described. 
The  fact  that  lid-spasm  was  elicited  as  described  he  could  not  consider 
as  evidence  of  a  retinal  injury,  since  it  is  well  known  that  such  reflexes 
are  easily  produced  by  harmless  light  on  the  dark  adapted  eye.  Aside, 
then,  from  injury  to  the  retina  by  the  range  of  rays  mentioned,  a  mere 
change  of  intensity  would  account  for  the  lid-spasm  since  Helmholtz 
has  shown  that  fluorescent  light  is  many  times  as  intense,  physiologi- 
cally, as  the  light  producing  it.  As  to  the  diminution  of  fluorescence 
with  age  Birch-Hirschfeld  considered  the  question  still  open,  since  he 
found  the  fluorescing  power  of  the  lens  of  an  individual  70  years  old 


776  WALKER. 

undiminished.  Further  he  regarded  fluorescence  of  the  nature  of  a 
catalytic  chemical  reaction  if  it  was  to  be  considered  chemical  at  all, 
emphasizing  the  fact  that  no  chemical  basis  for  this  phenomenon 
had  ever  been  established.  Against  the  proposition  that  fluorescence 
decreased  with  the  length  of  time  of  exposure,  he  cited  an  experiment 
in  which  he  exposed  and  fluoresced  the  rabbit's  lens  continuously 
for  five  or  six  hours  with  no  noticeable  change  in  intensity  of  fluo- 
rescence whatever.  He  objected  to  drawing  any  conclusions  from 
the  lens  of  a  gliomic  eye  since  the  presence  of  a  pathological  condition 
might  readily  alter  the  properties  of  the  lens  although  it  was  appar- 
ently normal. 

Later  in  1909  Schanz  and  Stockhausen316  by  means  of  Wood's 
light  filter  which  absorbs  the  rays  below  375  MM  were  able  to  make 
further  investigations  on  the  range  of  fluorescing  rays  in  the  same 
manner  previously  employed.  This  filter  inhibited  the  fluorescence 
very  little  so  that  the  range  most  effective  in  producing  fluorescence 
was  placed  at  375  MM  to  400  MM-  The  fresh  clear  lenses  from  eyes 
removed  by  tumor  or  absolute  glaucoma  were  used.  The  absorption 
power  of  the  cornea  and  lens  in  these  cases  were  studied  by  photo- 
spectrographic  methods  with  a  quartz  glass  optical  system  in  the 
usual  manner.  From  a  study  of  these  photographs  they  agreed  with 
Birch-Hirschfeld  that  the  cornea  had  a  greater  absorption  power  than 
glass  and  considered  that  the  effectual  absorption  amounted  to  320  MM 
as  mentioned  under  cornea.  That  absorption  in  the  lens  was  increased 
by  age  was  further  confirmed. 

Schanz  and  Stockhausen318  further  investigated  the  phenomena  of 
fluorescence  with  the  result  that  they  retracted  their  previous  idea 
that  fluorescence  represents  a  separate  spectral  color  lavender-gray, 
and  returned  to  the  theory  of  Helmholtz  that  it  is  made  up  of  rays  of 
various  length  as  is  ordinary  mixed  or  white  light.  They  used  the 
crossed  prism  or  crossed  spectrum  method  of  Newton  to  analyze  the 
fluorescent  light  in  the  following  manner.  With  a  quartz  glass  optical 
system,  the  light  from  an  arc  light  was  concentrated  on  a  prism,  the 
resulting  spectrum  was  rendered  linear  by  focussing  it  on  a  screen 
with  a  cylindrical  lens,  axis  parallel  to  the  length  of  the  spectrum. 
Now  when  thin  layers  of  fresh  human  lens  were  laid  on  the  scjeen  in 
various  regions  of  the  spectrum  fluorescence  was  noted  to  begin  in  the 
blue  region,  become  more  intense  in  the  violet  region,  and  was  strong- 
est of  all  in  the  ultra  violet  region  between  370  MM  and  400  MM-  Below 
370  MM  fluorescence  diminished  slowly.  The  maximum  point  of  fluo- 
rescence was  at  385  MM-  This  fluorescent  light  was  further  analyzed 


EFFECTS   OF   KADIANT   ENERGY   ON  THE   EYE. 


777 


by  a  second  prism  placed  at  right  angles  to  the  first  prism  and  parallel 
with  the  first  spectrum.  The  second  spectrum  seen  through  the 
second  prism  showed  at  once  that  the  fluorescent  light  was  made  up 
of  rays  of  different  length.  Of  these  the  greater  portion  were  green 
waves,  a  less  portion  of  blue  waves,  while  a  considerable  amount  of  red 
was  also  present.  In  the  light  of  these  findings  and  after  a  further 
study  a  few  months  later  the  following  tabulation  of  the  effect  of  light 
waves  on  the  eye  was  prepared : 


Visib 
red  to  green 
I 
760MM-490AIM 

e  light 
blue  to  violet 
II 

490MM-400MM 

Invisibl 

III 

400M^-375MM 

e  ultra  violet  light 

IV 

375/i«Ai-320MM 

V 

320MM-OMM 

These  rays 

A  small  part  in- 

A   part    fluoresces 

Take  little  part 

Do       not 

proceed  un- 

creasing      with 

the    lens.     A    part 

in       fluorescing 

penetrate 

changed  to 

age    is    by    the 

fluoresces    the    re- 

the    lens.     Are 

through 

the     retina 

lens     absorbed, 

tina.     A  part  pro- 

intensely      ab- 

the cornea 

and         are 

and  is  concerned 

ceeds  unchanged  to 

sorbed    by    the 

but      pro- 

visible. 

in     its     fluores- 

the  light   sensitive 

lens,      reaching 

duce  outer 

cence.    Another 

retina.        Whether 

the  retina  only 

eye 

part     fluoresces 

the   appearance   of 

in    young    eyes 

trouble. 

the   retina   and 

the     lavender-gray 

much  weakened. 

the  rest  is  seen 

is  due  to  a  direct 

by  the  retina  as 

stimulation    or    by 

blue  and  violet. 

intermediation      of 

fluorescence  is  un- 

known. 

Hallauer 152  in  1909  spectrophotographically  measured  the  absorp- 
tive power  of  over  100  fresh  human  lenses  and  found  it  to  depend 
mostly  on  individual  differences  of  thickness,  color  and  consistency. 
For  young  lenses,  while  most  of  the  rays  were  absorbed  at  about  400  MM> 
a  certain  number  of  more  or  less  weakened  rays  between  330  MM  and 
315  MM  were  able  to  pass  through.  The  effect  of  severe  or  chronic 
illness  in  these  cases  was  to  increase  the  amount  of  all  to  pass  through 
in  the  latter  region.  Also  in  advanced  age,  where  the  absorption  lay 
usually  between  400  MM  and  420  MM>  the  effect  of  severe  reducing 
diseases  was  to  reduce  the  absorption  power  to  about  375  MM- 

Martin238  in  1912  found  the  absorption  power  of  lens  suspended 
in  normal  salt  solution  to  begin  at  400  MM  and  become  complete  at 
350  MM- 


778  WALKER. 


INJURIES  TO  THE  LENS. 

Czerny  85  in  1867  in  his  blinding  experiments  with  sun's  rays  noted 
turbidity  in  the  lens  cortex  but  no  change  in  the  lens  capsule.  Deutsch- 
man89  repeating  these  experiments  in  1882  got  the  same  results. 
Herzog 176  in  1903  obtained  similar  results  with  the  carbon  arc,  glass 
lenses  and  heat  filters.  These  lens  changes  were  undoubtedly  due 
to  the  thermic  action  of  visible  rays. 

Widmark  417  in  his  experiments  on  the  outer  eye,  1889-1892,  with 
the  1200  c.  p.  arc  light  noted  lens  changes  microscopically.  These 
he  did  not  find  when  ultra  violet  rays  were  screened  out  by  a  quinine 
sulphate  solution  therefore  he  concluded  they  were  the  etiological 
factor.  Ogneff259  in  1896  repeated  this  experiment  with  a  6000  to 
8000  c.  p.  arc  lamp  at  a  distance  of  50  cm.  to  1  meter  for  15  to  20  min. 
but  found  no  lens  trouble  though  all  the  conjunctival  corneal  and  iris 
troubles  were  present. 

Widmark418  repeated  his  work  again  in  1901  using  a  4000  c.  p.  zinc 
arc  in  much  the  same  way  with  the  same  results.  Two  rabbits  A  &  B 
were  exposed  to  the  same  arc  light  at  the  same  time.  In  the  case  A 
the  light  traversed  two  glass  lenses  separated  by  5  to  6  cm.  of  a  10% 
quinine  sulphate  solution.  The  distance  from  arc  to  lenses  was  13.6 
cm.  and  light  was  concentrated  on  the  dilated  rabbit's  eye  6  cm. 
beyond  the  lenses.  Ultra  violet  rays  and  heat  rays  were  cut  out  by 
this  method  and  no  lens  changes  were  found.  In  case  B  the  conditions 
were  the  same  except  that  the  lenses  were  of  quartz,  separated  by 
water.  In  this  case  in  addition  to  the  usual  disturbance  in  the  outer 
eye  and  iris,  the  lens  capsule  in  the  pupillary  area  showed  at  first 
intense  staining  of  the  nuclei,  mitosis,  cell  proliferation  and  destruc- 
tion. There  was  swelling  of  lens  fibre  bundles  with  partial  destruction. 
Also  transudate  between  the  cortex  and  capsule. 

In  1904  with  a  3£  to  4^  amp.  Finsen  light,  Birch-Hirschfeld 38 
could  not  get  lens  changes  after  5  to  10  min.  exposures.  Hertel 168  in 
26  rabbits  used  in  the  previously  mentioned  experiment,  and  also 
Strebel 359  failed  to  get  lens  changes,  though  the  usual  outer  eye  and 
iris  changes  were  produced  as  previously  observed. 

Hess 174  in  1907  used  a  3^  amp.  uviol  mercury  vapor  lamp  with  a 
65  cm.  tube.  He  exposed  1  to  16  hours  at  a  distance  of  10  to  30  cm. 
The  animals  used  were  rabbits,  guinea-pigs  and  frogs.  He  found 
outspoken  lens  changes  as  described  by  Widmark.  These  lens  changes 
appeared  about  48  hours  after  a  6  to  12  hour  exposure.  Surrounding 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         779 

the  central  damaged  area  but  under  cover  of  the  iris  was  a  ring  or 
"wall"  of  deeply  stained  cells  crowded  together  perhaps  by  the  swollen 
central  cells,  first  damaged.  These  changes  appeared  in  the  pupillary 
region  and  would  show  regeneration  as  indicated  by  numerous  mitotic 
figures  in  the  course  of  2  to  4  days,  if  no  further  or  stronger  exposure 
was  made.  He  found  that  interposition  of  glass  plates  cutting  out 
rays  below  313  ju;u  or  even  280  /JL/JL  prevented  lens  trouble.  He  agreed 
with  Widmark  in  thinking  the  glass  blower's  cataract  due  to  ultra 
violet  light. 

Birch-Hirschfeld 78,  however,  took  up  this  point  in  1909.  He  ex- 
posed a  rabbit's  eye  for  5  minutes  at  a  time  on  three  successive  days 
to  the  light  from  a  5  amp.  arc  light  which  traversed  first  a  "  Euphos- 
glas"  and  was  then  concentrated  with  a  20  diopter  common  glass  lens. 
No  heat  filter  was  used.  On  the  4th  day  he  found  on  microscopical 
examination  the  same  lens  changes  recorded  by  Widmark  and  Hess. 
Therefore  he  concluded  that  rays  in  the  neighborhood  of  400  MJ.  must 
be  responsible,  and  that  probably  some  of  the  shorter  blue  and  violet 
rays  were  effective  as  well  as  the  longer  ultra  violet  rays.  Further  he 
argued  that  this  same  group  of  rays  was  in  all  probability  responsible 
for  the  production  of  the  glass  blowers  cataract  and  possibly  also  for 
the  production  of  the  senile  cataract,  though  this  latter  he  regarded 
as  far  from  proven  (cf.  page  677). 

Without  experimental  evidence  Wenzel418  in  1806,  von  Beer  in  1817 
and  Plenk  in  1877  84  pointed  out  the  disposition  to  cataract  among 
glass  blowers,  and  Meyhofer 245  in  1886,  found  the  percentage  to  be 
11.6  in  glass  blowers  under  40  years  old.  These  cataracts  commonly 
began  on  the  left  side  which  was  most  severely  exposed  to  the  heat. 
Robinson  298  and  Stein 349  later  confirmed  these  findings. 

Schanz  and  Stockhausen  32°  in  1910,  measured  the  quantity  and 
quality  of  the  radiations  from  the  glass  blowers  furnace,  and  the 
temperatures  to  which  his  head  was  subjected  at  different  stages  of 
his  work.  By  accurate  spectro-photographic  measurements  of  the 
light  at  the  distance  at  which  the  glass  blower  worked,  they  found  the 
spectrum  to  be  especially  strong  in  the  region  from  400  ^u  to  350  /zju, 
shading  down  to  320  nfj,  below  which  there  were  no  rays.  At  once 
they  considered  they  had  the  explanation  why  these  people  had  lens 
trouble  without  anterior  eye  trouble.  The  worker's  head  was  exposed 
to  a  temperature  of  110  degrees  C.  in  taking  the  glass  from  the  oven 
and  to  45  degrees  C.  during  the  process  of  blowing.  This  temperature, 
while  it  might  be  a  factor,  is  not  so  great  as  that  to  which  many  iron 
and  blast  furnace  workers  are  exposed  without  receiving  any  eye 


780  WALKER. 

injuries.  Temperature,  therefore,  they  thought  not  nearly  so  much 
to  blame  as  the  ultra  violet  rays  from  400  MM  to  350  MM  which  fluoresce 
the  lens  most  strongly.  The  absence  of  rays  below  320  MM  accounted 
for  the  absence  of  outer  eye  trouble,  in  answer  to  the  question  raised 
by  Birch-Hirschfeld  during  the  previous  year.  In  comparing  the 
cataracts  of  glass  blowers  and  those  produced  artificially  by  the  arc 
light,  they  noted  as  has  Widmark418,  Hess178,  Cramer81  and  others, 
as  well  as  Stein  349  later,  that  they  both  begin  in  the  pupillary  region, 
but  that  while  the  artificially  produced  cataracts  begin  usually  on  the 
anterior  pole,  the  glass  maker's  cataract  starts  usually  on  the  poste- 
rior pole.  For  the  posterior  polar  variety  no  better  explanation  could 
be  offered  at  that  time  than  that  of  Cramer  81,  who  believed  them  to  be 
the  result  of  the  greater  concentration  of  chemical  rays  at  that  point 
due  to  the  refractive  power  of  the  eye  media  anterior  to  that  point. 
Other  theories  were  concentration  of  the  chamber  fluids  (Leber221) 
and  increased  venous  stasis  (Peters272).  However  Snell343  in  Eng- 
land found  cataract  no  more  common  among  glass  blowers  than  among 
other  laborers,  and  Robinson  298  found  the  percentage  increasing  above 
normal  only  among  the  finishers  working  with  very  heavy  metal 
glasses,  after  long  service. 

In  1909,  Handmann 157  submitted  an  extensive  statistical  study  of 
senile  cataracts.  Hirschberg  confirmed  by  Schulek330  had  first  sug- 
gested the  intense  sunlight  as  a  factor,  in  the  country  and  India, 
and  had  noted  the  early  appearance  in  the  lower  quadrant.  Handman 
was  able  to  prove  that  the  senile  cataract  particularly  of  India  for 
the  most  part  81%  (previously  given  by  Greene  146  as  95%),  begins 
in  the  lower  quadrant  of  the  lens.  This  region  of  the  lens  was  found 
to  be  more  deeply  yellow  colored,  and  therefore  had  a  higher  absorp- 
tive power  for  ultra  violet.  The  ultra  violet  content  of  light  coming 
from  the  sky  at  such  an  angle  as  to  strike  this  quadrant  is  far  greater 
than  that  reflected  into  the  eye  from  the  broken  surfaces  below,  thus 
supporting  the  original  idea  of  Schwitzer  332  that  abiotic  rays  were  an 
etiological  factor.  Presumptive  evidence  at  least  was  furnished  to 
explain  the  senile  cataract.  Schanz  and  Stockhausen  322  at  once  ac- 
cepted these  findings  as  giving  the  key  to  the  etiology  of  a  large  group 
of  senile  cataracts.  But  Birch-Hirschfeld32  pointed  out  that  dwellers 
in  mountainous  and  snowy  regions  of  high  ultra  violet  content  were 
not  prone  to  cataract  and  considered  that  the  shorter  visible  rays 
could  not  be  excluded  here  as  in  other  cases,  and  Hess 184  from  a 
mathematical  standpoint  considered  that  rays  not  obstructed  by  the 
lids  and  eyelashes  could  not  reach  the  lower  quadrant  of  the  lens  in 
sufficient  quantity  to  account  for  the  condition. 


EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         781 

Martin 238  in  1912,  with  a  single  high  intensity  exposure, —  one  half 
to  two  hours  at  a  distance  of  one  inch  from  a  Kromayer  water-cooled 
mercury  vapor  lamp,  found  the  lens  capsule  changes  as  described  by 
Hess.  Because  the  interposition  of  a  benzol  cell  prevented  these 
changes  they  were  ascribed  to  ultra  violet  light.  With  repeated 
exposures  of  moderate  intensity  without  lid  retractors  —  at  a  distance 
of  4  inches  to  3  ft.  at  intervals  of  1  to  2  weeks  over  a  period  of  1\  to  12 
months  exposure  times  varying  from  1  to  3  hours,  the  following 
changes  were  noted.  In  one  rabbit  of  this  latter  series  exposed  every 
10  days  at  4  in.  distance  for  1  hour  over  a  period  of  3  to  12  months  lens 
changes  somewhat  as  described  by  Hess  were  found,  but  differed  in 
that  the  "wall"  was  wider,  the  central  cells  were  uninjured,  and 
proliferation  was  2  or  3  cells  thick.  There  was  present  in  all  of  this 
series  slight  corneal  opacities.  Others  of  the  series,  less  severely 
exposed,  had  no  corneal  opacities  or  lens  trouble,  while  those  more 
severely  exposed, —  3  hours  every  2  weeks  at  4  inches  for  3  to  11 
months, —  showed  dense  corneal  opacities  which  had  undergone  vas- 
cularization  but  the  lenses  were  clear  and  capsule  normal,  supposedly 
protected  by  the  dense  corneal  opacities. 

Sharply  to  be  distinguished  from  these  are  cataracts  experimentally 
produced  by  exposure  to  light,  are  those  resulting  from  the  actual 
transit  of  the  electric  current  through  or  near  the  eye.  Leber221 
in  1882  first  explained,  the  long  noted  tendency  to  cataract  in  people 
struck  by  lightning,  as  due  to  the  electro-chemical  reaction.  This 
was  experimentally  demonstrated  by  Hess  117  in  1888  who  made  an 
electric  spark  to  impinge  in  the  supraorbital  region  of  a  rabbit.  He 
noted  a  central  destruction  of  lens  epithelium  and  vacuolization  of 
lens  fibres  with  a  marked  secondary  peripheral  mitosis  and  prolifera- 
tion of  the  lens  epithelium  resulting  in  the  formation  of  equatorial 
cataracts.  Likewise  Kiribuchi 203  in  1900  using  the  Leyden  condenser 
spark  produced  the  same  results.  Clinically  many  cases  of  cataract 
after  lightning  stroke  or  short  circuit  have  been  reported  as  due  to 
ultra  violet  rays  but  really  must  be  included  in  this  last  group.  Birch- 
Hirschfeld 38  in  1909  found,  in  a  study  of  all  such  cases  reported  up  to 
that  time,  injuries  such  as  burns  and  cicatricial  formations  or  impair- 
ment of  nutrition  or  nerve  supply,  which  would  readily  account  for 
cataract  formation.  These  cataracts  are  further  distinguished  by 
the  fact  that  clinically  and  experimentally  they  do  not  appear  centrally 
as  do  those  in  purely  blinding  experiments  but  peripherally.  Again 
on  an  experimental  basis  the  length  of  exposure  time  is  seldom  if  ever 
long  enough.  No  cases  of  lens  trouble  from  lightning  without  bodily 


782  WALKER. 

injury  have  been  reported.  Essentially  the  same  is  true  in  blinding 
due  to  short-circuit  arcs,  though  sometimes  it  is  difficult  to  distinguish 
mechanical  from  light  effects,  as  in  cases  reported  by  Grimsdale  and 
James 198  and  by  Posey  282  in  1911. 


THE  RETINA:  INJURIES,  SCOTOMATA,  ERYTHROPSIA. 

That  blindness  may  result  from  direct  observation  of  the  sun  of 
eclipses,  has  been  known  without  doubt  for  ages.  Indeed  Galileo 31 
is  known  to  have  injured  his  eyes  by  observation  of  the  sun  with  his 
telescope.  Galen 129  cites  cases  of  blinding,  with  more  or  less  subse- 
quent return  of  vision,  in  observers  of  eclipses  of  the  sun.  He  also 
noted  that  central  scotomata  or  blind  spots  often  resulted  in  the 
same  way.  Reid294  in  1761  and  Soemmering 342  in  1791  according  to 
Hess 184  probably  gave  the  first  accurate  description  of  the  subjec- 
tive phenomena  of  sun  blinding. 

Less  frequently  the  same  ocular  disturbances  have  also  long  been 
noted  in  seamen  long  exposed  to  strong  reflection  of  the  sun's  rays 
from  water  surfaces.  Likewise  travelers  over  desert  or  glary  plains 
are  not  uncommonly  afflicted  with  these  visual  disturbances. 

Czerny  85  as  early  as  1867  showed  that  a  lesion  of  the  retina  of  the 
rabbit  visible  with  the  ophthalmoscope  could  be  produced  by  the  sun's 
rays.  Coccius,  Ruete,  in  1853,  and  Jaeger  in  1854,  had  already 
described  the  ophthalmoscopic  changes  in  the  human  eye.  Czerny 
threw,  by  use  of  a  concave  mirror,  and  glass  lens  system  concentrated 
sun's  rays  which  had  traveled  a  20  cm.  water  heat  filtering  tube,  into 
the  eye  of  the  rabbit  for  10  to  15  sec.  The  region  of  the  retinal 
image  on  exposure  was  found  to  be  whitened  and  seared.  A  section 
under  the  microscope  showed  what  he  described  as  a  coagulation  of 
the  albuminous  substances  of  the  retinal  elements. 

On  the  17th  of  May,  1882,  there  was  an  eclipse  of  the  sun  which  in  a 
few  days  brought  four  cases  of  sun  blinding  into  Leber's  clinic  in 
Gottingen.  Deutschmann  89  at  once  reported  them  with  a  repetition 
of  Czerny's  experiment  in  which  he  fully  confirmed  Czerny's  findings. 
One  of  the  four  cases  used  a  smoke  glass  to  observe  through  and 
another  a  blue  glass,  but  each  received  severe  injury  nevertheless. 
On  ophthalmoscopic  examination  all  four  cases  showed  a  character- 
istic appearance  of  the  macular  region  varying  somewhat  in  degree 
corresponding  with  the  degree  of  injury.  In  his  experiments  Deutsch- 
mann arranged  a  convex  lens  to  transmit  the  sun's  rays  reflected  from 


EFFECTS   OF   KADIANT   ENERGY   ON  THE   EYE.  783 

a  concave  mirror.  The  distance  separating  the  two  was  equal  to  the 
sum  of  their  focal  lengths  so  that  parallel  light  was  thrown  into  the 
atropinized  eye  of  the  rabbit.  Even  after  a  second's  exposure  a 
silvery  white  spot  round  to  oval  in  shape,  covered  the  retinal  image 
region.  It  was  surrounded  by  a  brownish  ring.  Longer  exposure 
enlarged  the  silvery  central  spot  and  the  surrounding  rings  became 
paler  and  took  on  a  silvery  sheen.  Microscopic  section  showed 
droplets  and  clumping  of  the  coagulated  albumins  of  the  retinal  cells. 
Surrounding  and  below  these  areas  were  exudative  and  then  hypere- 
mic  areas.  The  choroidal  pigment  was  increased  and  showed  a 
tendency  to  wander.  Indeed  there  was  so  much  similarity  to  early 
stages  of  choroiditis  disseminata  that  he  was  the  first  to  consider  the 
possibility  that  heat  and  light  rays  may  be  an  etiological  factor  in 
the  latter  disease.  However  Aubaret  190°,  Hess 1902,  and  Garten 1908 
have  since  attempted,  without  success,  to  prove  this  proposition.  To 
determine  the  influence  of  heat  Deutschmann  passed  the  rays  through 
a  tube  of  clear  running  water  20  cm.  long.  The  changes  could  be 
produced  but  it  always  took  a  few  minutes  longer.  Therefore  he 
concluded  that  both  heat  and  light  are  active  as  etiological  factors. 
In  none  of  these  cases  with  short  exposure  times  were  outer  eye  troubles 
noted. 

In  1892  Widmark413  repeated  Czerny's  and  Deutschmann's  work 
with  a  1200  c.  p.  arc  light.  The  exposure  time  was  2-12  hours,  usually 
4  hours.  With  the  10%  quinine  sulphate  filter  to  remove  ultra  violet 
light  he  found  much  less  retinal  trouble  than  with  the  quartz  glass 
system.  Also  less  effect  through  yellow  bichromate  filters  than 
through  blue,  so  that  he  concluded  that  blue  violet  and  ultra  violet 
rays  were  most  effective. 

Herzog 176  in  1903  reported  that  he  had  repeated  the  work  of  Czerny 
and  Deutschmann  in  1898  and  found  that  the  circumscribed  retinal 
lesions  could  be  effected  in  |  second.  A  similar  but  more  diffuse 
retinal  change  could  be  produced  in  ^  to  2  hours  with  a  15  amp.  arc 
light  whose  rays  were  concentrated  on  the  rabbit's  eye  after  traveling 
a  28  cm.  tube  of  alum  water.  Further  similarity  in  action  was  noted 
in  the  production  in  two  or  three  old  rabbits  of  an  opaque  cataractous 
condition  of  the  lens  visible  to  the  eye  as  Czerny  and  Deutschmann 
had  noted.  When  the  cornea  was  continuously  irrigated  with  normal 
salt  solution  to  avoid  overheating,  the  result  was  a  cloudy  swelling 
of  the  epithelium  which  was  less  transparent  than  the  simple  des- 
quamation  that  resulted  without  the  excess  of  moisture.  All  these 
changes,  including  the  cataract  formation  already  described  he  ascribed 
to  light  transformation  to  heat,  and  not  to  ultra  violet  light. 


784  WALKER. 

However,  Aubaret 6  in  1900  was  inclined  to  disregard  heating  effects 
in  sunblinding  since  he  found  a  thermometer  held  in  sunlight  concen- 
trated by  40  D  diaphragmed  lens,  only  registered  1°  to  2°  increase  in 
temperature.  But  Birch-Hirschfeld 38  showed  that  50°  paraffin  in 
thin  layers  on  black  paper  was  melted  in  a  few  seconds  when  exposed 
to  sunlight  as  the  retina  would  be  in  sunblinding  but  when  white 
paper  was  used  under  the  same  conditions  several  minutes  were  re- 
quired to  melt  the  paraffin,  thus  demonstrating  the  effect  of  black 
retinal  pigment  in  absorbing  heat. 

The  phenomenon  of  light  adaptation  and  the  effect  of  various  wave 
lengths  of  light  on  the  retina  has  been  studied  by  a  number  of  observers, 
Mann235,  Kuhne276,  Pergens269,  Nagel257,  van  Genderen-Stort 137, 
and  more  recently  by  Hess182,  Birch-Hirschfeld39  and  others.  Van 
Genderen-Stort 137  in  1887  showed  that  pigment  wandering  in  the 
choroid  and  retina  was  least  active  in  yellow  light  and  this  finding 
called  attention  to  the  value  of  yellow  glasses  as  protection  for  the 
eyes.  He  further  amplified  the  knowledge  of  the  effect  of  light  on 
the  finer  structures  of  the  retina  of  the  dark  adapted  eye.  When  such 
an  eye  is  exposed  to  light  he  showed  that  the  pigment  cells  just  out- 
side the  rods  and  cones  send  down  processes,  apparently  between  the 
rods,  which  carry  with  them  much  pigment  and  thus  tend  to  isolate 
optically  the  rods  from  each  other.  At  the  same  time  the  cones  tend 
to  escape  this  isolation  somewhat  by  moving  in  the  same  direction 
towards  the  light.  Another  change  found  to  take  place  was  the 
bleaching  of  the  visual  purple  found  in  the  outer  part  of  the  rods  in  the 
dark  adapted  eye. 

The  effect  of  ultra  violet  ray  and  light  fatigue  on  the  finer  struc- 
tures of  the  retina  has  been  studied  by  Widmark412,  Czerny85, 
Deutschmann 89,  Ogneff259,  Bach14,  Stebel359,  Kiribuchi 203,  and 
Terrien  364.  Except  for  the  last  three,  who  found  a  very  slight  gang- 
lion cell  chromatolysis,  their  results  were  negative,  which  Birch- 
Hirschfeld37  later  thought  was  due  to  insufficient  light  intensities 
having  been  used.  In  snow  blinding  nothing  more  than  hyperemia 
of  the  retina  and  optic  disc  have  been  reported  (Reich92,  1880). 

Birch-Hirschfeld37  in  1904  made  some  experiments  on  rabbits  in 
which  he  claimed  to  have  produced  definite  pathological  changes  by 
exposing  the  eyes  to  ultra  violet  light.  In  his  first  series  of  experiments 
he  separated  out  the  ultra  violet  light  from  a  15  ampere  carbon  arc 
light  by  means  of  a  quartz  prism,  and  obtained  retinal  changes  only 
in  eyes  from  which  he  had  removed  the  lenses.  In  his  second  series 
he  used  the  direct  light  from  a  3  to  4.5  ampere  water  cooled  Finsen 


EFFECTS   OF    RADIANT    ENERGY   ON   THE   EYE.  785 

iron  arc  and  obtained  well  marked  changes,  notably  chromatolysis 
and  vacuolization  of  the  ganglion  cells,  in  lens  containing  eyes  as  well 
as  in  two  aphakic  eyes.  These  experiments  are  described  and  dis- 
cussed in  detail  on  page  687. 

From  the  foregoing  experiments  Birch-Hirschfeld  concluded  that 
the  lens  did  not  afford  complete  protection  to  the  retina  from  the 
specific  action  of  ultra  violet  light.  Best 27,  however,  took  the  view 
that  no  danger  to  the  retina  was  to  be  feared  from  ultra  violet  light 
since  he  found  he  was  able  to  look  at  the  sun  directly  without  deleteri- 
ous effects  for  ten  seconds  through  a  blue  uviol  glass  which  transmits 
freely  the  ultra  violet  waves  from  the  sun,  but  absorbs  all  visible 
waves  longer  than  about  470  n/j.  in  length. 

Birch-Hirschfeld  35  in  1908  reported  five  cases  of  visual  disturbance 
among  workers  in  mercury  vapor  illumination.  He  concluded  that 
after  long  occupation  with  unprotected  eyes  in  mercury  vapor  arc- 
light  a  disturbance  of  retinal  function  may  result  with  or  without  an 
electric  ophthalmia  or  a  similar  conjunctival  reaction.  These  in- 
juries took  the  form  of  pericentral  scotomata  for  red  and  green.  By 
the  aid  of  a  Priestly  Smith  scotometer  these  scotomata  were  mapped 
out.  The  affected  region  had  a  sector  or  ring-formed  shape  at  a 
distance  of  15  degrees  to  20  degrees  from  the  fixation  point.  Red 
usually  appeared  yellowish  and  green  as  a  gray  or  even  white.  The 
central  color  vision  was  only  in  two  cases  injured  in  the  sense  of  red- 
green  blindness,  though  floating  spots  often  temporarily  obscured  the 
fixation  point.  The  color  scotomata  disappeared  in  the  course  of  a 
few  weeks  if  protecting  glasses  were  worn  or  if  work  in  ultra  violet 
light  was  abandoned. 

The  solar  eclipse  seen  in  Europe  on  the  17th  of  April,  1912,  afforded 
excellent  opportunities  for  observation  of  ophthalmoscopic  and  func- 
tional retinal  changes  due  to  sun  blinding.  In  the  series  of  50  reported 
by  Birch-Hirschfeld41,  four  cases  showed  normal  eye  grounds,  19 
others  had  increased  foveal  reflex,  with  frequently  a  concentric  irregu- 
lar reddish-brown  area,  which  in  eleven  cases  cleared  up  at  the  end  of 
a  wTeek.  In  16  other  cases  there  was  noted  irregular  pigmentation  of 
the  macula  and  small  gray  puntiform  spots  or  globules  which  remained 
unaltered  for  months.  In  31  cases  an  absolute  central  and  in  19  cases 
an  absolute  paracentral  scotoma  was  found  which  afterwards  became 
relative  scotomas.  The  rest  had  relative  central  scotomas  to  begin 
with.  These  were  mostly  eccentric  downward  extending  1°  to  10° 
The  majority  of  cases  with  the  milder  injuries  regained  almost  normal 
visual  acuity  in  the  course  of  a  few  weeks.  In  small  numbers  of  single 


786  WALKER. 

cases  numerous  previous  observers 184,  Vinsonneau,  Stocke,  Pergens 
v.  Pflugk,  Arlt,  Lescarret,  Menacho,  Villard,  found  similar  changes. 
Lamhofer  in  1912  found  a  chorioretinal  exudate  with  pigmentation 
and  at  the  same  time  Best  reported  a  case  with  decreased  peripheral 
field  and  adaptation.  Erythropsia  has  also  been  noted  by  Birch- 
Hirschfeld  and  by  Braunschweig. 

In  26  out  of  36  cases  of  sun  blinding  in  the  eclipse  of  1912,  Jess  20° 
working  in  Hess's  clinic  found  a  ring-scotoma  20°  to  40°  from  the 
fixation  point.  In  this  ring  formed  area,  white  appeared  gray,  and 
colors  were  not  seen  in  a  few  cases,  in  others  red  was  called  yellowish, 
green  was  called  gray,  and  blue  was  called  yellow.  In  the  course  of  a 
week  the  damage  gradually  decreased  until  only  a  small  semicircular 
area  of  scotoma  was  left  below.  Hess 184  states  that  this  finding  has 
been  verified  by  Peppmueller,  Pergens,  and  Hoppe.  Speleer  found 
enlargement  of  the  blind-spot  ring-scotoma  and  concentric  contraction 
of  the  field  after  sun  blinding.  Birsch-Hirschfeld 43,  however,  has 
taken  exception  to  the  ring-scotoma  of  Jess,  finding  that  it  was  a 
normal  phenomenon  and  not  specially  related  to  eclipse-blindness. 

The  large  number  of  functional  impairments  due  to  lightning  and 
short-circuit  flashes  cannot  be  referred  definitely  to  any  given  range 
of  wave  lengths.  These  derangements  have  been  reported  in  great 
numbers  and  variations.  There  may  be  permanent  blindness  or 
temporary  blindness  in  one  or  both  eyes.  Central  and  peripheral 
scotomata  are  more  common  and  while  usually  temporary  they  may 
be  permanent.  Hancock 156  in  1907  reported  a  case  of  ring-scotoma. 
Disturbances  of  color  vision  are  very  common  but  temporary.  These 
include  erythropsia,  red  blindness,  red  green  and  blue  green  blindness 
and  scotomata.  Ophthalmoscopic  examination  may  show  nothing 
even  in  severe  cases  or  there  may  be  punctate  spots  in  the  macula  as 
in  sun  blinding,  Uhthoff  375,  Haab  «,  Terrien  365.  Birch-Hirschfeld  31 
considers  rays  from  350  MM  to  400  n/j,  most  active  in  producing  these 
disturbances  with  probably  even  more  assistance  from  blue  and  violet 
rays  because  of  the  greater  intensity. 

While  usually  there  is  outer  eye  trouble  in  these  cases  a  few  have 
reported  functional  disturbances  without  photophthalmia.  Nelson 
Dering184  Le  Roux  and  Renaud225  Maclean234  and  Purtscher289. 

In  snow  blinding  functional  disturbances  have  been  noted  to  take 
the  form  of  temporary  amblyopia  (Widmark 412  citing  Enald)  night- 
blindness  (Widmark412)  and  day  blindness.  In  1907  Best  &  Haenel 29 
found  after  snowblinding  a  central  scotoma  for  red  and  green  extend- 
ing about  10°  from  the  fixation  point.  This  disturbance  disappeared 
in  the  course  of  six  weeks. 


EFFECTS   OF   RADIANT   ENERGY   ON   THE   EYE.  787 

Very  recently  Behr17  has  found  marked  reduction  in  the  light 
adaptation  power  in  four  patients  complaining  of  visual  disturbances 
after  continued  work  by  arc  light  and  strong  incandescent  lights. 
They  noted  that  after  working  by  these  lights  and  then  moving  to  a 
darker  part  of  the  room  that  they  could  hardly  see  to  work  at  all, 
or  on  coming  out  into  sunlight  everything  appeared  gray  or  dark. 
In  twilight  or  after  a  rest  in  darkness  the  vision  improved  slowly  only 
to  receive  another  setback  on  further  exposure  to  the  artificial  light. 
These  patients  were  tested  on  the  Piper  instrument  for  measuring  the 
dark  adaptation  power.  Normally  as  Piper  has  shown  there  is  a  slow 
increase  of  sensitiveness  during  the  first  61  to  10  min.  in  the  dark 
and  then  a  sudden  marked  increase  in  30  to  35  min.  followed  by  a 
further  slow  increase  until  after  45  min.  the  maximum  light  per- 
ception sensitiveness  is  reached.  Behr  found  in  none  of  these  cases 
was  there  much  increase  of  sensitiveness  after  10  min.  and  at  the 
end  of  45  min.  was  still  g  to  j  of  normal.  These  cases  were  advised 
to  work  less  by  strong  artificial  lights  and  Euphos  glas  was  prescribed. 
Mild  light  such  as  oil  lamplight  was  advised  where  possible.  Three 
of  the  patients  were  presumably  cured  because  they  made  no  further 
complaint,  while  the  fourth  whose  case  was  followed,  regained  in  a 
short  time  a  light  adaptation  that  was  better  than  normal. 


ERYTHROPSIA  OR  RED  VISION. 

Hildige171  in  1861  noted  erythropsia  in  snow  blinding.  Mayer- 
hausen241  and  Steiner350  in  1882  reported  cases  after  blinding  by 
lightning  and  short  circuiting  and  by  the  sun's  rays  both  directly  and 
indirectly  as  from  water  surfaces  or  from  snow.  Cases  which  occurred 
after  cataract  operations  were  further  reported  by  Dimmer92  and 
Putscher 287  in  1883.  Widmark  in  his  correlation  of  electric  ophthal- 
mia and  snow  blinding  noted  that  erythropsia  occurred  in  both  but 
did  not  investigate  the  subject  further.  Fuchs  126  in  his  monograph 
of  1896  emphasized  the  role  of  ultra  violet  light  in  all  these  cases  espe- 
cially in  cases  of  snow  blinding,  aphakia,  and  electric  ophthalmia. 
Using  the  fact  that  established  by  Kuhne216  and  Konig  two  years 
before,  that  the  visual  purple  is  most  rapidly  bleached  by  rays  below 
500  nfj..  Fuchs  advanced  the  theory  that  the  regenerating  visual 
purple  accounted  for  the  red  vision  as  an  entopic  phenomenon. 
Schulek329  produced  Erythropsia  by  observing  spectral  ultra  violet 


788  WALKER. 

light,  also  Birch-Hirschfeld  did  the  same  while  working  with  the 
Schott-light.  However,  Vogt 397  in  1908  dilated  his  own  pupil  and 
after  producing  erythropsia  by  observing  a  sunlit  snow  field  found  no 
decrease  in  the  red  vision  when  he  went  into  a  room  illuminated  only 
by  a  light  whose  red  rays  had  all  been  screened  out  by  an  Erioviridin 
filter.  Vogt397  in  1908  and  also  Wydler 422  in  1912  considered  ery- 
thropsia as  the  red  phase  of  the  after  picture  of  the  intense  white 
surface.  Best27  in  1909  agreed  with  Vogt's  view  and  considered 
erythropsia  due  to  visible  rays  since  he  could  produce  it  by  looking  at  a 
snow  surface  through  a  yellow  glass  cutting  out  rays  below  400  nn 
but  not  with  a  blue  uviol  glass.  However  Birch-Hirschfeld31  could 
not  consider  that  ultra  violet  rays  were  relieved  of  responsibility 
entirely  since  the  wide  pupil  alone  of  the  aphakic  eye  could  hardly 
account  for  erythropsia,  as  Vogt  held,  by  admitting  a  greater  quantity 
of  light.  He  therefore  concluded  that  invisible  as  well  as  visible  rays 
were  active  in  the  etiology  of  erythropsia. 

Rivers296  in  1901,  advanced  a  theory  as  to  the  red  color  based  on 
an  observation  made  by  Briiche  in  1851  that  the  eye  under  normal 
conditions  is  more  or  less  completely  adapted  for  red.  Rivers  attri- 
butes the  color  in  erythropsia  to  the  blood  in  the  anterior  retinal 
layers.  Schoute184  objected  to  this  theory  on  the  basis  that  Pur- 
kinje's  experiment  of  the  entopic  vision  of  retinal  vessels  shows  that 
light  is  absorbed  by  the  blood  and  they  give  dark  shadows. 


PROTECTIVE  GLASSES. 

In  1900  Schulek  33°  first  studied  the  means  of  protecting  the  eyes 
against  ultra  violet  rays  and  found  that  solutions  of  Triphenylme- 
thane  in  xylol  and  Nitrobenzol  in  Alcohol  had  the  highest  absorptive 
power  of  the  transparent  media  examined.  These  liquids  absorbed 
practically  all  rays  below  396  /*/*.  He  suggested  that  these  solutions 
be  enclosed  in  flat  oval  shaped  glass  chambers  made  to  fit  the  eyes 
and  to  protect  them  from  injuries  due  to  ultra  violet  radiations. 

Stearkle348,  Vogt396  and  Hallauer153  studied  the  absorptive  prop- 
erties of  blue  uviol,  yellowish  and  smoky  gray  glasses.  The  last 
named  worker  produced  a  glass  mixture  by  a  secret  process  the  so 
called  "  Hallauerglas."  After  a  similar  study,  Fieuzal 119  produced 
in  like  manner  Fieuzelglass,  which  however,  was  not  greatly  used  on 
account  of  its  color.  Also  a  yellow-green  glass  patented  under  the 


EFFECTS   OF   RADIANT   ENERGY   ON   THE   EYE.  789 

name  of  Enixanthosglas  was  offered  as  well  as  a  variety  of  the  modi- 
fications by  glass  manufacturers.  Here  again  the  color  was  not  satis- 
factory. 

Schanz  and  Stockhausen 309,  after  finding  that  electric  ophthalmia 
could  be  produced  through  18  mm.  of  common  glass  as  has  been  men- 
tioned, began  to  study  glass  manufacture  in  the  hope  of  producing  a 
colorless  glass  of  high  ultra  violet  absorption  power  for  general  use. 
In  1909  they  produced  and  patented  a  glass  of  higher  absorptive  power 
than  hard  flint  and  called  it  "  Euphosglas."  At  first  it  was  made  in 
grades  1,  2,  3,  and  4,  but  recently  other  grades  have  been  added.  It 
has  a  light  yellowish  green  tinge  and  fluoresces  in  ultra  violet  light. 

Birch-Hirschfeld 38  in  1909  studied  photometrically  the  absorption 
power  of  these  and  other  glasses  with  considerable  accuracy.  In  the 
same  year  Vogt 304  compared  a  new  and  very  hard  flint  glass  produced 
by  Schott  with  his  absorptive  solutions  and  was  surprised  to  find  that 
it  had  about  the  same  efficiency,  beginning  to  absorb  at  405  up.  and 
giving  practically  complete  absorption  below  396  nn. 

In  1909  Hallauer155  measured  photometrically  the  absorptive  power 
of  the  various  protective  glasses  available  at  that  time.  The  thick- 
ness varied  from  1  to  3  mm.  and  exposure  time  of  one  minute. .  The 
average  results  follow. 

Common  glass  absorbs  to  295  juju 

Blue  glass  "  300 

Lead  glass  "  305 

Smokey  gray  "         "  325 

"Gonin"  glass  "         "  330 

Schott's  heavy  flint  "         "  340 

Fieuzal  yellow  glass  "         "  375 

Enixanthos  glass  "  380 

Euphos  gray  glass  "  390 

Euphos  green  glass  "         "  390 

Hallauer  glass   #64        "         "  420 

As  glasses  became  available  to  cut  out  various  wave  lengths  the 
question  arose  as  to  what  spectral  range  constituted  the  best  illumina- 
tion. 

Voege's388  answer  to  this  question  in  1908  raised  a  considerable 
controversy.  He  maintained  that  the  light  from  the  clouds  or  clear 
sky  had  been  for  ages  the  normal  illumination  for  the  eyes,  but  never- 
theless contained  a  considerable  amount  of  ultra  violet  light  as  low  as 


790  WALKER. 

300  nn  in  wave  length.  He  examined  the  spectra  of  various  high 
power  are  lights  with  opal  and  milk  glass  shades  or  coverings.  These 
spectra  compared  very  closely  with  that  of  cloud  light. 

Hertel  and  Henker172  in  support  of  this  view  carried  out  a  very 
accurate  set  of  measurements,  in  the  laboratory  of  C.  Zeiss,  Jena,  of 
the  cloud  and  skylight  spectrum,  of  variously  covered  or  shaded  high 
power  arc  lights  and  of  the  percentage  of  penetrability  and  absorp- 
tion power  of  various  glasses  for  wave  lengths  in  different  parts  of  the 
spectrum.  The  spectrum  of  the  clouds  or  clear  sky  was  found  to 
contain  no  rays  below  300  /zju  and  very  few  below  310  /*/*. 

Having  what  they  considered  an  ideal  light  the  next  question  was 
in  what  manner  should  the  artificial  lights  be  compared  with  it.  In 
producing  injurious  effects  on  animals  they  noted  that  unprotected 
lights  of  very  great  intensity  had  been  used  under  conditions  never 
found  in  modern  lighting  systems  therefore  previous  observers  had 
studied  entirely  atypical  conditions  and  not  the  conditions  to  which 
human  eyes  are  really  exposed.  Widmark  had  used  a  1200-4000  c.  p. 
arc  light  without  covering  at  a  distance  of  25  cm.  from  the  animal's 
eye  for  length  of  time  ranging  from  2-4  hours  and  longer.  Likewise 
Birch-Hirschfeld  had  used  similar  arc  lights  with  and  without  disper- 
sion through  a  prism  usually  at  a  distance  of  10  cm.  to  20  cm.  Hess 
had  used  a  Schott  uviol  lamp  65  cm.  long  of  3-3|  amp.  The  animals 
were  at  a  distance  of  10  cm.  to  20  cm.  and  the  time  of  exposure  1-16 
hours.  These  data  represented  the  average  experimental  conditions 
necessary  to  produce  injuries  but  not  at  all  the  conditions  to  which 
mankind  is  at  present  exposed. 

Therefore  they  considered  a  far  better  criterion  for  practical  pur- 
poses would  be  accurately  to  photograph  the  spectrum  of  arc  lights  at 
the  minimum  distance  of  actual  service  in  lighting,  and  to  find  whether 
or  not  such  globes  or  mantles  can  be  placed  around  the  light  source  as 
to  render  the  spectrum,  in  quantity  and  quality,  within  the  range  of 
the  cloud  or  skylight  spectrum. 

Accordingly  the  lights  were  placed  50  cm.  to  100  cm.  distant  from 
the  spectroscope  opening.  The  optical  system  of  the  spectroscope 
was  made  of  quartz  glass.  The  effect  of  indirect  illumination  and  of 
half  spherical  or  inverted  bowl  shaped  shades  for  increasing  horizontal 
illumination,  was  also  measured  by  raising  the  light  and  its  shade 
about  40  cm.  above  the  axis  of  the  spectroscope  condenser. 

In  all  cases  under  these  conditions  by  use  of  the  usual  milk  glass 
and  opal  glass  shades  they  had  no  difficulty  in  getting  a  spectrum 
comparing  in  quantity  and  quality  very  closely  with  the  spectrum  of 


EFFECTS   OF   RADIANT   ENERGY  ON  THE   EYE.  791 

cloud  light  and  entirely  within  the  spectrum  obtained  from  ordinary 
Welsbach  gas  mantle  lights  with  ordinary  clear  glass  shades.  They 
used  a  variety  of  lights  including  flaming  arc  and  mercury  vapor  arc 
lights. 

The  absorptive  power  of  various  other  glasses  proposed  for  this 
purpose,  by  their  inventors  was  determined  by  use  of  the  most  ac- 
curate available  method.  In  the  visible  part  of  the  spectrum  the 
absorptive  power  was  determined  by  use  of  a  polarizing  spectrophoto- 
meter  with  crossed  Nicol's  prisms,  while  in  the  ultra  violet  region  the 
same  instrument  was  used  with  optical  parts  of  quartz  glass.  The 
results  are  tabulated  below  in  terms  of  percentage  of  penetrability  of 
various  wave  lengths.  The  absorption  power  is  obtained  by  simply 
subtracting  these  results  from  100.  In  all  these  cases  a  thickness  of 
glass  of  1  mm.  was  used  indicated  by  A',  except  in  the  case  of  the 
very  dense  Neutralglas  which  was  measured  in  thicknesses  of  0.1  mm. 
indicated  by  A0'1. 

Concerning  protective  glasses  for  the  eyes,  Hertel  and  Henker 
believe  the  same  criterion  should  be  followed,  namely,  that  the  best 
glass  is  the  one  which  will  reduce  the  spectrum  of  the  particular  light 
to  which  the  eyes  are  exposed  to  the  closest  possible  approximation 
to  the  spectrum  of  cloud  and  sky  light.  For  observation  of  the 
strongest  arc  lights  at  close  range,  the  condition  under  which  certain 
workmen  are  placed,  they  consider  the  Neutralglas  F  3815,  of  Schott  to 
be  the  best.  With  this  glass,  in  layers  thinner  than  any  other  glass, 
one  may  observe  directly  the  bare  20  amp.  arc  light  at  50  cm.  without 
injury  since  the  spectrum  is  about  the  same  as  that  of  cloud  light 
minus  the  ultra  violet  portion.  The  thickness  of  Hallauerglas  No.  64 
necessary  to  give  the  same  results  as  Neutralglas  of  0.8  mm.,  was  9.0 
mm. ;  and  of  Euphosglas  No.  4  was  38  mm. 

Next  to  Neutral  glas,  for  this  purpose  stood  the  smoky  or  Rauch- 
glas  No.  276  and  Sonnenglas  No.  66  of  the  Fredener  glass  works. 
After  these  came  Hallauerglas  No.  66,  while  Hallauerglas  No.  62  and 
No.  64  and  Euphosglas  Nos.  1,  2,  3  and  4,  were  not  strong  enough  in 
absorptive  power. 

Schanz  and  Stockhausen 321  at  once  criticised  the  above  work, 
objecting  particularly  to  the  premises  on  which  the  decisions  were 
based,  namely  that  skylight  or  cloud  light  can  be  taken  as  the  ideal 
light.  Against  this  view  was  cited  particularly  the  work  of  Hand- 
mann  showing  that  a  very  large  group  of  cataracts  begin  in  the  quad- 
rant of  the  lens  most  exposed  to  the  light  of  the  sky  during  life.  Since 
it  was  definitely  known  and  admitted  by  all  that  certain  injuries  to 


792 


WALKER. 


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EFFECTS  OF  RADIANT   ENERGY  ON  THE  EYE.  793 

the  eye  could  be  produced  by  ultra  violet  light,  any  light  containing 
these  rays  could  not  be  considered  ideal  light.  The  positive  findings, 
previously  mentioned  of  pathological  changes  due  to  ultra  violet  light, 
violet  and  perhaps  blue  rays,  such  as  the  glass  blower's  cataract, 
erythropsia,  blindness  permanent  and  temporary,  and  scotomata  as 
well  as  other  functional  retinal  disturbances,  they  held  to  be  against 
the  assumption  that  light  containing  considerable  amounts  of  ultra 
violet,  violet  and  blue  rays,  can  be  considered  ideal  and  harmless. 
Further  minor  objections  were  made  to  the  exposure  time  used  in 
photographing  the  different  light  sources  and  it  was  pointed  out  that 
their  newer  glasses  "Euphosglas  A"  and  "Euphosglas  B,"  more 
suitable  for  technical  purposes,  had  not  been  examined. 


794  VERHOEFF,    BELL,   AND   WALKER. 


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EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.          797 

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129  GALEX,  De  usu  partium,  lib.  10,  cap.  3. 

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131  GALEZOWSKY,  Des  Ophtalmes  electriques,  Rec  d'Opht.,  1902,  p.  521. 
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134  GARTEX,  Die  Veranderungen  der  Netzhaut  durch  Licht,  Handb.  d.  ges. 

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136  GAYET,  Sur  le  pouvoir  absorbant  du  Cristallin  pour  les  rayons  ultraviolets, 

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139  GIXSBURG,  Ein  Fall  von  Blitzstar,  Westnik  ophth.,  1906,  p.  14. 

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148  GRIMSDALE   and  JAMES,   A  Case  of  Cataract  from  an  Electric  Shock, 

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149  GUTZMAXX,   Zwei  Falle  von  Blitzkatarakt,   Wiener  Klin.   Wochenschr., 

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150  HAAB,  Traumatische  Makula-Erkrankung  bewirkt  durch  den  elektrischen 

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153  HALLAUER,  Einige  Gesichtspunkte  fur  die  Wahl  des  Brillen  materials, 

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154  HALLAUER,  Spectrographic  Studies  concerning  the  Limits  of  absorption  of 

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155  HALLAUER,    Spectrographische    Untersuchungen    liber    die    absorption- 

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156  HANCOCK,   Ring  Scotoma,   Royal  London  Ophthal.   Hospital   Reports, 

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157  HANDMANN,  Uber  den  Beginn  des  Alterstars  in  den  unteren  Linsenhalfte, 

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158  HECKEL,  Electric  ophthalmia,  Opht.  Rec.,  1905,  p.  500. 

159  HECKEL,  Report  of  a  Case  of  electric  ophthalmia,  Amer.  Jour,  of  Oph., 

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160  HEIBERG  UND  GRONHOLM,  Histologische  Untersuchungen  iiber  die  Ein- 

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162  HELMHOLTZ,  Handb.  der  physiologischen  Optik,  1896. 

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164  HENRI,  Helbrouner,  et  de  Recklinghausen,  Nouvelle  Lampe  a  rayonement 

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167  HERTEL,  Experimentelles  liber  ultraviolettes  Licht,  Ber.  d.  31,  Vers.  d. 

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168  HERTEL,  Uber  Beeinflussung  des  Organismen  durch  Licht,  speziell  durch 

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170  HERTEL,  Einiges  liber  die  Empfindlichkeit  des  Auges  gegen  Lichtstrahlen, 

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171  HERTEL,   Experimentelles  und   Klinisches  liber  die   anwendung  lokaler 

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172  HERTEL  und  HENKER,  Uber  die  Schadlickheit  und  Brauchbarkeit  unserer 

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173  HERTEL,  Uber  lichtbiologische  Fragen.  Zeitschr.  f.  Augenh.,  1911. 

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175  HERTEL,  Uber  die  Einwirkung  von  Lichtstrahlen  auf  den  Zellteilungs- 

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176  HERZOG,  Diskussion  zum  Vortrag  Birch-Hirschfeld,  Bericht  d.  ophth.  Ges. 

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177  HESS,   Experimentelles   liber   Blitzkatarakt,    Internat.  ophthalm  Kongs, 

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178  HESS,  Uber  die  Wirkung  ultraviolettes  Strahlen  auf  die  Linse,  Munch. 

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179  HESS,  Versuche  liber  die  Einwirkung  ultra violetten  Lichtes  auf  die  Linse, 

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180  HESS,   Uber   "  Blaublendheit "   durch   Gelbfarbung  der   Linse,   Arch.   f. 

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181  HESS,  Weitere  Mitteilungen  uber  die  Gelbfarbung  der  menschlichen  Linse 

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182  HESS,  tlber  den  Farbensinn   im   indirekten  Sehen,  Arch.   f.  Ophth.,  36, 

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183  HESS,  Pathologie  der  Linse,  Graefe-Samisch.  Handbuch,  p.  179. 

184  HESS,  tlber  Schadigungen  des  Auges  durch  Licht,  Arch.  f.  Augenh.,  1913, 

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185  HESSBERG,  Ein  weiterer  Beitrag  zu  den  Augenverletzungen  durch  Blitz- 

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186  HEWETSOX,  Remarks  on  acute  inflammation after  witnessing  electric 

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187  HEWETSOX,  Danger  to  the  eyes  during  electric  welding  etc.,  Lancet,  2, 

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188  HEYDT,  A  Case  of  so-called  Bottle-makers'  Cataract,  Ophth.  Record,  1911, 

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189  HILBERT,  Zur  Kenntnis  der  Augenverletzungen  durch  Blitz,  Wochenschr. 

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190  HILL,  Two  cases  of  electric  blindness,  Lancet,  2,  194  (1897). 

191  HILDIGE,  Fall  von  Schneeblindheit,  Med.  Times  and  Gaz.,  1861. 

192  HIRSCHBERG,  tlber  den  Star  der  Glasblaser,   Zentralbl.  f.  Augenheilk, 

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193  HIRSCHLER,  Zur  Rotsehen  der  aphakischen,  Wien.  med.  Wochenschr.,  4, 

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194  HOFFMAX,  Uber  die  Schneeblindheit,  und  einige  verwandte  Blendungs- 

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195  HOPPE,    Augenschadigung    durch    die    Sonnenfinsternis    vom    17    April, 

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196  ISAKOWITZ,   Augenerkrankung   durch    Sonnenblendung,    Deutsche    med. 

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197  IWANOFF,  Les  consequences  de  la  foudre  sur  la  vision,  Soc.  franc  d'opht.,  11, 

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198  JAXSSEX,  Sur  1'absorption  de  la  chaleur  rayonnante  obscure  dans  les  milieux 

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199  JESS,  Verh.  d.  physikal.-med.  Gesellschaft  Wiirzburg,  1912.     Also  Miinch. 

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200  JESS,  Die  Ringskotome  nach  Sonnenblendung,  Arch.  f.  Augenheilk.,  1913, 

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201  JOXES,  The  effects  of  electric  light  on  the  eye,  Ophthalm.  Rev.,  1883,  p.  106. 

202  JUXITJS,    tlber    Unfallverletzungen    insondere    Augenkrankungen    durch 

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203  KIRIBUCHI,  Experimentelle  Untersuchungen  uber  Katarakt  und  sonstige 

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204  KLUG,  Du  Bois,  Reymond's  Arch,  f .  Physiol.,  1878,  p.  246. 

205  KXAPP,  Bilateral  Macular  disease  after  Short  Circuit,  Zeitschr.  f.  Augenh., 

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206  KXIES,  Ein  Fall  von  Augenverletzung  durch  Blitzschlag,  Arc.  f.  Ophth. 

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207  KOELSCH,  Der  Augenschutz  in  Glashiitten,  Miinch.  med.  Wochenschr., 

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208  KOLLXER,  Die  Klinische  Diagnose  der  erwerbenen  Violettblindheit,  Berl. 

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209  KOSTER,  Verslag  over  einige  experim.  betr.  de  erythropsie,  Nederl.  Tijdechr. 

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210  KRAMER,   Ursachlicher  Zusammenhang  zwischen  einer  Augenkrankung 

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211  KREIBICH,  Die  Wirkung  des  Sonnenlichtes  auf  Haut  und  Conjunctiva, 

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212  KRETSCHMER,  Verletzung  durch  elektrischen  Strom,  Zentralbl.  f.  Augenh., 

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212»  KRIENES,  Einfluss  des  Lichtes  auf  das  Auge,  in  physiologischer  und  patho- 
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213  KROTOW,  Zur  Wirkung  der  Hallauerschen  Schutzglaser,  Westnick  Ophth., 

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213»  KRUCKMANN  AND  TELEMANX,  Investigation  of  temperature  of  various  parts 
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214  KRUSS,   Die   Durchlassigheit  einer  Anzahl  Jenaer  optischer  Glaser  fur 

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215  KTJBLI,  Vier  Falle  von  Erythropsie,  Arch.  f.  Augenh.,  18,  p.  258. 

216  KUHNE,  tlber  das  Vorkommen  des  Sehpurpurs,  Zentralbl.  f.  med.  Wissen- 

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217  KUWABARA,  Zur  Pathogenese  des  Blitzstares,   Arch.  f.  Augenh.,    62,    1 

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218  LAKER,  Ein  neuer  Fall  von  Augenaffektionen  durch  Blitzschlag,  Arch.  f. 

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219  LARSEN,  tJber  die  Intensitat  der  Sonnenstrahlen,  Finsens  Mitteil.,  1,  1900, 

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220  DE  LAROQUETTE,  Solar  Erythema  and  Pigmentation,  Le  Monde  Medicale, 

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221  LEBER,  tJber  Katarakt  und  sonstige  Affektionen  durch  Blitzschlag,  Arch. 

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222  LEBER,  Die  Ernahrungs  und  Cirkulations  Verhaltnisse  der  Auges,  Graefe- 

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222»  LEFRANC,  Contribution  a  l'6tude  de  la  lumiere  et  de  la  Chaleur,  considered 
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223  LE  Roux,  Cataracte  par  de"charge  electrique,  Arch,  d'opht.,  1902,  p.  626. 

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225  LE  Roux  ET  RENAUD,  Sur  un  cas  de  photo-traumatisme  oculaire  par  la 

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226  LESCARRET,  Des  scotomes  pas  eclipse  solaire.     These  Bordeaux,  1900. 

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229  LITTLE,  The  effect  of  electric  light  on  the  eye,  Ophthalmic  Review,  1883, 

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230  LUCKIESH,  Radiant  Energy  and  the  Eye,  Electrical  World,  Oct.  25,  1913. 
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231  LUNDSGAARD,  Zwei  Falle  von  Verletzungen  des  Auges  durch  electrischen 

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232  MACKAY,  On  blinding  of  the  retina  by  direct  sunlight,  Ophthalmic  Review, 

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233  MAKLAKOFF,  Influence  de  la  lumiere  voltaique  sur  les  teguments  du  corps 

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EFFECTS    OF   RADIANT    ENERGY   ON   THE    EYE.  803 

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272  PETERS,  Weitere  Beitrage  zur  Pathologie  der  Linse,  Monatsbl.  f.  Augen- 

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273  PFAHL,   Erfahrungen  liber   Verletzungen   durch   Blitz   und  Elektrizitat, 

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279  PLAUT,   tlber   die    Ursache    des    Blitz-Keratoconus,   Kim.   Monatsbl.   f. 

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280  PLITT,  tlber  den  Fruhjahrskatarrh  der  Augen  und  den  atiologischen  Ein- 

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289  PURTSCHER,   Ein   Fall  von   Augenaffektion  durch  Blitzschlag,   Arch.   f. 

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290  RAYNER-BATTEN,  Eclipse  blinding  with  obstruction  of  a  retinal  artery  and 

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292  REICH,  Die  Neurose    des   nervosen    Sehapparates,  hervorgerufen  durch 

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294  REID,  An  inquiry  into  the  human  mind  on  the  principles  of  common  sense, 

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295  v.  REUSSE,  Beitrag  zur  Kenntnis  der  Erythropsie,  Arch.  f.  Augenh.,  62, 

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296  RIVERS,  Injury  to  the  Eye  from  a  large   charge  of  electricity,  Arch,  of 

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297  ROEMER,  Zur  Frage  des  Blendungsschmerzes,  Zeitschr.  f.  Augenh.,  8, 

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298  ROBINSON,  On  bottle-makers  cataract,  Brit.  med.  Jour.,  1907,  p.  381. 

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300  ROCKLIFFE,  The  effect  of  electric  light  on  the  eye,  Ophthalm.  Rev.,  1883. 

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302  ROY,  Effect  of  intense  flashes  of  light  upon  the  eye,  Alabama  Med.  Journ., 

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303  RYERSON,  Lightning  stroke  causing  eye  diseases,  Med.  Rec.  April,  1899. 
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305  SAUER,  Experimente  iiber  die  Lichtbarkeit  ultravioletter  Strahlen,  Ann.  d. 

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306  SAUTTER,  Electric  Injuries  of  the  Eye,  Ophth.  Rec.,  1911,  p.  238. 

307  SCHANZ,  Veranderungen  u.  Schadigungen  d.  Auges  durch  Licht,  Deutsch. 

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308  SCHANZ,  Demonstration  des  durch  ultrayiolette  Strahlen  zu  erzeugenden 

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309  SCHANZ  u.  STOCKHAUSEN,  Wie  schutzen  wir  unserer  Augen  vor  der  Ein- 

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310  SCHANZ  u.  STOCKHAUSEN,  Durch  des  uv.  Licht.  der  modern  kunstlichen 

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311  SCHANZ  u.  STOCKHAUSEN,  Die  Schadigung  des  Auges  durch  Einwirkung 

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312  SCHANZ  u.  STOCKHAUSEN,  Zur  Beurteilung  der  Schadigung  des  Auges 

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806  VERHOEFF,    BELL,    AND   WALKER. 

313  SCHANZ  u.  STOCKHAUSEN,  Die  Wirkung  der  ultravioletten  Lichtstrahlen 

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314  SCHANZ  u.  STOCKHAUSEN,  Schutz  gewerblicher  Arbeiten  gegen  Blendung 

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315  SCHANZ  u.  STOCKHAUSEN,  fiber  die  Wirkung  der  Ultravioletten  Strahlen 

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316  SCHANZ  u.  STOCKHAUSEN,  Wie  schutzen  wir  unsere  augen  von  die  Ein- 

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317  SCHANZ  u.  STOCKHAUSEN.  Uber  Blendung,  Arch.  f.  Ophth.,  71,  175  (1909). 

318  SCHANZ  u.  STOCKHAUSEN,  Uber  die  Fluorescenz  der  Linse,  Arch,  f .  Ophthal. 

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319  SCHANZ  u.  STOCKHAUSEN,  Weiterer  liber  Blendung,  Arch.  f.  Ophth.,  73, 

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320  SCHANZ  u.  STOCKHAUSEN,  Zur  Enstehung  des  Glasmacherstars,  Arch.  f. 

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321  SCHANZ  u.  STOCKHAUSEN,  Uber  die  Schadlichkeiten  und  Brauchbarkeit 

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322  SCHANZ  u.  STOCKHAUSEN,  Schutz    der   Augen   gegen   die    schadigenden 

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323  SCHIELE,  Friihjahrekatarrh  der  Conjunctiva,  Arch.  f.  Augenh.,  19,  281 

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324  SCHIESS-GEMUSENS,  Uber  Schneeblindheit,  Arch  f.  Ophth.,  26,  p.  3. 

325  SCHJERNING,    Uber    die    Absorption    der    ultravioletten    Strahlen    durch 

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326  SCHLEICHER,  Bin  Fall  von  Katarakt  nach  Blitzschlag,  Mitteilung  a.  d. 

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327  SCHNELLER,  Zur  Kasuistik  der  Chorioretinitis  nach  Uberblendung,  Arch,  f . 

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328  SCHUELER,    Uber    Blendung   nach    Beobachtung   einer   Sonnenfinsternis, 

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329  SCHULEK,  Die  Erythropsie,  Ungar.  Beitr.  z.  Augenheilk.,  1,  101  (1895). 

330  SCHULEK,  Schutzbrillen  gegen  Ultravioletten  auf  Grund  photologischer 

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331  SCHWITZER,  Beitrage  zur  Entstehung  des  grauen  Alterstares,  Ungar.  Beitr. 

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332  SCHWITZER,  Uber  die  Aetiologie  des  grauen  Stares,  Orvosi  Hetilap.  Szemes- 

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333  SEABROOK,  Amber  yellow  glass  in  the  examination  and  treatment  of  eyes, 

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334  SEKULIC,  Ultraviolette  Strahlen  sind  unmittelbar  sichtbar,  Ann.  d.  Physik 

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335  SERVAIS,  Observation  de  cataracte  produite  par  la  foudre,  Ann.  d'Ocul., 

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336  SETSCHENOW,  Uber  die  Fluoreszenz  der  durchsichtigen  Augenmedien  beim 

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337  SILEX,  Beitrag  zur  Casuistik  der  Augenaffectionen  in  Folge  von  Blitzschlag, 

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338  SILFVAST,  Ein  Fall  durch  Blitzschlag  hervorgerufener  Lasionen  der  Augen, 

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339  SMITH,  A  Scotometer,  Ophth.  Rev.,  1906,  p.  155. 

340  SNELL,  Sun  blindness  of  the  retina,  Brit.  med.  Jour.,  Jan.  18,  1902. 

341  SNELLEN,  Erythrppsie,  Arch.  f.  Ophth.,  44,  p.  1. 

342  SOEMMERING,  Pflichten  gegen  die  Augen.,  1791. 


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343  SORET,  Sur  la  visibilite  des  rayons  ultraviolettes,  Compt.  rend,  de  1'Acad. 

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344  SORET,  Sur  1' absorption  des  rayons  ultraviolets  par  les  milieux  de  1'oeil  et 

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345  SORET,  Sur  la  transparence  des  milieux  de  1'oeil  pour  les  rayons  ultra- 

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346  SORET,  Archives  des  Sciences  Phys.  et.  Naturelles,  Recherches  sur  1'ab- 

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347  SPELEERS,  Gesichtsfeldaufnahmen  bei  Ringskotom  durch  Sonnenfinsternis, 

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348  STAERKLE,  Uber  die  Schadlichkeit  moderner  Lichtquellen  auf  das  Auge 

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349  STEIN,  Untersuchungen  uber  Glasblaserstar,  Arch.  f.  Augenh.,  74, 53  (1913). 

350  STEINER,  Zur  Kenntnis  der  Erythropsie,  Wien.  med.  Presse,  1882,  No.  44. 

351  STEINHEIM,  Zur  Kasuistikder  Erythropsie,  Zentralbl.  f.  Augenh.,  1884, 

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352  STERN  AND  HESSE,  Uber  die  Wirkung  des  Violettlichtes  auf  die  Haut, 

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353  STIGELL,  Uber  Blendung  der  Netzhaut,  Diss.  Strassburg,  1883. 

354  STOCKE,    Sonneneklipse    Skotome.     Viaamsch    Natur   en    Geneeskundig 

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355  STOCKHAUSEN,  Blendung,  ihre  Ursache  und  Wirkung,  Zeitschr.  f.  Beleuch- 

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356  STOCKHAUSEN,  Die  Beleuchtung  von  Arbeitsplatzen  und  Arbeitsraumen, 

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359  STROBEL,  Lichttherapie  und  Augenheilkunde,  75  Vers.  deutschen  Natur- 

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359"  STUBEL,  Fluorescence  of  animal  tissues  in  ultraviolet  light,  Pfluges.  Arch, 
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360  SULZER,  Vier  Falle  von  Retinaaffektion  durch  direkte  Beobachungen  der 

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361  SWEET,  Electric  Burn  of  Eyes.     (Section  on  Ophth.  College  of  Physic. 

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362  TALKO,  Contusion  des  Auges  durch  Blitz,  Zeitschr.  f.  Augenh.,  5,  p.  484. 

363  TERRIER,  Ophthalmic  electrique,  Arch.  d'Ophth.,  8,  1  (1888). 

364  TERRIEN,   Cataracte  par  decharge  electrique,   Arch.   d'Ophth.,   28,  679 

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365  TERRIEN,  Du  prognostic  des  troubles  visuels  d'organism  ele'ctrique,  Arch. 

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066  TIGERSTEDT,  Die  Grenzen  des  sichtbaren  Spektrums,  Biophysikalisches 
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367  TOCZYSKI,  Bin  ungewohnlicher  Fall  von  Augenverletzung  durch  Blitz- 

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368  TRENDELENBURG,  Uber  die  Bleichung  des  Sehpurpurs  mit  spektrahlen. 

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1904,  No.  24. 

369  TSCHERMAK,  Die  Hell-Dunkel-Adaptation  des  Auges,  Ergebn.  d.  Physiol. 

Asher-  Spiro,  1902. 

370  TYNDALL,  Das  Licht,  Deutsche  Ausgabe,  Braunschweig,  1876,  p.  177-192. 

371  TYNDALL,  Ueber  leuchteude  und  dunkele  Strahlung,  Pogg.  Ann.  124,  36 

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808  VERHOEFF,   BELL,   AND   WALKER. 

372  UHLE,  Anamie  des  Nervus  opticus  und  Retina  durch  Blitzschlag,  Klin, 

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373  UHTHOFF,  Ein  Fall  von  einseitiger  zentraler  Blendung-Retinitis  durch 

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374  UHTHOFF,  Blitzschlagwirkung  auf  das  Auge,  Deutsch.  med.  Wochenschr.. 

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375  UHTHOFF,  Zur  zentralen  Blendungsretinitis  bei  Beobachtung  der  Sonnen- 

finsternis   1912,   Sitzungsber,   der  wissensch.  Akad.  d.  Augenarzte 
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376  UHTHOFF,  Friihjahrskatarrh,  Arch.  f.  Ophth.,  29,  177. 

377  ULBRICH,  Optikusatrophe  nach  Einwirkung  eines  elektrischen  Stromes, 

Zentralbl.  f.  Augenh.,  1900,  p.  264. 

378  VALOIS,  Ophtalmie  electrique,  Clin.  ophth.,  1904,  p.  92. 

379  VALOIS  ET  LEMOINE,  Troubles  visuels  consecutifs  a  1'observation  directe 

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380  VALUDE,  L'erythropsie,  Paris,  Steinheil,  1888. 

381  VAN  LINT,  Accidents  oculaires  provoques  par  1'electricite,  Rapport  presente 

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382  VERHOEFF,  Ultra  violet  light  as  a  germicidal  agent.     Experimental  in- 

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383  VERHAEGHE,  Cataracte  par  coup  de  foudre,  Gaz.  des  Hopitaux,   1905, 

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384  VETSCH,  Friihjahrskatarrh  der  Conjunctiva,  Inaug.  Disert.,  Zurich,  1879, 

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385  VILLARD,  Troubles  oculaires  consecutifs  a  1'observation  directe  des  eclipses 

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386  VILLARD,    Augenstorungen   nach   direkter   Beobachtung  von   Sonnenfin- 

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387  VINSONNEAU,  Scotome  par  eclipse  solaire  et  le'sion  maculaire,  Arch,  d'opht., 

Sept.,  1912. 

388  VOEGE,  1st  durch  das  uv.  Licht  der  modernen  kiinstlichen  Lichtquellen 

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389  VOEGE,  Bemerkungen  zu  den  Aufsatz  Schanz  und  Stockhausen:  Uber  die 

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390  VOEGE,  Die  Ultravioletten  Strahlen  der  kiinstlichen  Lichtquellen  und  ihre 

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1910,  p.  14. 

391  VOEGE,  Uber  den  Schutz  des  Auges  gegen  die  Einwirkung  der  ultravioletten 

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392  VOEGE,  Uber  Licht  und  Warmestrahlung  der  kiinstlichen  Lichtquellen, 

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394  VOEGE,  A  Simple  Apparatus  for  the  Examination  of  the  Colour  and  Quality 

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395  VOEGE,  Need  we  fear  the  effects  of  the  ultra  violet  constituent  in  the  light 

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395»  VOEGEL,   Lichttherapie  in  prakt.  elektrotechnick,  Electrotech.  Zeitsch., 
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396  VOGT,  Schutz  des  Auges  gegen  die  Einwirkung  ultravioletten  Strahlen 

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EFFECTS  OF  RADIANT  ENERGY  ON  THE  EYE.         809 

397  VOGT,    Ursache   und    Wcsen    der  Erythropsie,  Bericht.   d.    ophth.    Ges 

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398  VOGT,  Bemerkungen  zu  der  Replik  von  Schanz  und  Stockhausen,  etc., 

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399  VOGT,  Erwiderung  auf  die  Arbeit  von  Best, 24  Klin.  Monatsbl.  f.  Augenh.. 

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400  VOGT,  Experiment.     Untersuchungen  uber  die  Durchlassigkeit  der  durch- 

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401  VOGT,  Einige  Messungen  der   Diathermasie  das  menschlichen  Augapfels 

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402  VOGT,  Kritik  der  Abhandlung  von  Schanz  und  Stockhausen  und  Best, 

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403  VOGT,  Beitrag  zu  der  Frage  der  Entstehung  der  Blendungserythropsie, 

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404  VOGT,  Schadliche  Lichtquellen  und  Schutzglaser  gegen  dieselben,  Med. 

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405  Vossius,  Ein  Fall  von  Blitzaffektion  des  Auges,  Beitr.  z.  Augenh.,  1892, 

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406  Vossius,  Uber  die  durch  Blitzschlag  bedingten  Augenaffektionen,  Berl. 

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407  Vossius,  Fall  von  Ophthalmia  electrica,  Berliner  klin.  Wochenschr.,  1886, 

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408  DE   WAELE,   Asthenopsie  nerveuse   par  lumiere   electrique.     Emploi   de 

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409  WEBSTER,  Fox  and  Gould,  Retinal  insensibility  to  ultraviolet  and  infra  red 

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410  WENDENBERG,  Schadigungen  des  Sehorgans  durch  Blendung  bei  Sonnen- 

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411  WIDMARK,  Uber  den  Einfluss  des  Lichtes  auf  die  vordern  Medien  des  Auges 

un  Haut-  Uber  die  Durchlassigkeit  der  Augen  fur  ultravioletten 
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412  WIDMARK,  Uber  Blendung  der  Netzhaut,  Skand.  Arch.,  4,  281  (1893). 

413  WIDMARK,  Uber  die  Durchdringlichkeit  der  Augen  Medien  fur  ultraviolette 

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414  WIDMARK,  Uber  den  Einfluss  des  Lichtes  auf  die  vorderen  Teile  des  Auges, 

Nord.  med.  Ak.,  21,  1889. 

415  WIDMARK,  Uber  den  Einfluss  des  Lichtes  auf  die  vordernen  Medien  des 

Auges,.  Skand.  Arch.,  1,  264  (1889). 

416  WIDMARK,  Uber  die  Grenze  des  sichtbaren  Spektrums  nach  der  violetten 

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418  WIDMARK,  Uber  den  Einfluss  des  Lichtes  auf  die  Linse,  Mitteil.  aus  d. 

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419  WILLIAMS,  Observations  on  the  Effect  of  the  Light  of  the  Mercury-vapour 

lamp  on  the  Eye,  Electrical  World,  Sept.,  1911. 

420  WOLFFBERG,  Electroopthalmie  und  Hysteric,  Wochenschr.  f.  Ther.  und 

Hyg.  d.  Auges,  1903. 

-421  WURDEMAN  AND  MURRAY,  Case  of  macular  retinitis  due  to  flash  of  electric 
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422  WYDLER,  Experim.  Unters.  uber  Blendungsnachbilder  u.  deren  Verhaltnis 

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423  ZICKENDRAHT,  Notiz  fur  die  Absorptiongrenzen  einiger  Glaser  im  Ultra- 

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810  VERHOEFF,   BELL,   AND  WALKER. 

424  ZIMMERMANN,  Beitrag  zur  Kenntnis  der  durch  intensives  Licht  hervor- 

gerufenen   Veranderung   des   Sehorganes,   Festschr.   d.   Stuttgarter 
arztl.,  Vereins.,  1897. 

425  ZIRM,  Ein  Fall  von  bleibenden,  ausgedehnten  Veranderungen  der  beiden 

Maculae  durch  direktes  Sonnenlicht.,  Arch.  f.  Ophth.,  60,  401  (1905) 

426  ZSCHIMMER,   t)ber  neue   Glasarten   von   gesteigerter  ultraviolett  durch- 

lassigkeit,  Zeitschr.  f.  Instrumenkunde.  1903,  No.  12. 

427  ZSCHIMMER,  Die  Physikalischen  Eigenschaften  des  Glases  als  Funktionen 

chemischen    Zusammenretzung,    Zeitschr.    f.    Elektrochemie,    1905. 
No.  38. 

428  ZSCHIMMER,   Diskussion  zum  Vortrag  Schanz,     Elektrotechn.   Zeitschr., 

1908,  p.  848. 


PLATE  1. 


FIGURE  1.  Exp.  69.  Mag- 
netite arc,  double  lens  system, 
no  screen,  exposure  20  min- 
utes. This  exposure  was 
about  200  times  the  liminal 
exposure  for  photophthalmia. 

Cornea  12  days  after  ex- 
posure. The  epithelium  has 
reformed.  The  stroma  is 
softened  down  to  Descemet's 
membrane.  The  unevenness 
of  the  corneal  surface  is  due  to 
the  irregular  shrinkage  of  the 
semiliquefied  tissue  in  the 
process  of  fixation.  Note 
that  the  effect  on  the  stroma  is  progressively  greater  and  more  widespread  towards  the 
external  surface.  Photo.  X  12. 


Fig.  l. 


FIGURE  2.  Exp.  81.  Mag- 
netite arc.  Double  lens  sys- 
tem, water  cell,  flint  glass 
screen  (305  MM))  exposure  1 
hour. 

Relatively  slight  heat  effect 
on  the  cornea  after  three  days. 
The  epithelium  is  intact  but 
the  endothelium  is  destroyed. 
The  corneal  corpuscles  are 
present  and  actively  prolif- 
erating in  the  anterior  layers, 
while  many  of  them  are  de- 
stroyed in  the  posterior  layers. 
Photo.  X  32. 


Fig.  2 


FIGURE  3.  Exp.  88.  Mag- 
netite arc.  Double  lens  sys- 
tem, no  water  cell.  Flint  glass 
screen  (315  MM),  exposure  1 
hour. 

Marked  heat  effect  on  cor- 
nea after  48  hours.  The 
epithelium  is  intact.  The 
stroma  is  swollen  to  twice  its 
normal  thickness  and  the  cor- 
puscles are  completely  de- 
stroyed in  the  most  exposed 
area.  At  the  periphery  the 
reappearance  of  the  corpuscles 
is  abrupt  and  they  are  in 
active  proliferation.  The  en- 
dothelium is  destroyed  over 
a  large  area.  Photo.  X  39. 


Fig.  3. 


811 


PLATE  2. 


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£ 


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Fig.  4. 


Fig.  5. 


FIGURE  4.  Normal  lens  capsular  epithelium  of  rabbit.  Flat  preparation. 
Photo.  X  264. 

FIGURE  5.  Exp.  55.  Magnetite  arc.  Single  lens  system,  crown  glass 
screen  (295  MM),  exposure  1  hour. 

Lens  capsular  epithelium  24  hours  after  exposure,  showing  marked  abiotic 
effects.  The  cells  are  swollen  and  most  of  them  contain  granules.  In  the 
photograph  the  basophilic  and  eosinophilic  granules  cannot  readily  be  dis- 
tinguished from  each  other.  Photo.  X  264. 


Fig.  6. 

FIGURE  6.  Exp.  67.  Magnetite  arc.  Double  lens  system,  no  screen, 
exposure  20  minutes,  about  200  times  the  liminal  exposure  for  photophthalmia. 

Lens  capsular  epithelium  48  hours  after  exposure,  showing  marked  abiotic 
effects.  The  darker  granules  in  the  cells  are  basophilic,  the  lighter,  eosino- 
philic. The  clear  spaces  in  this  and  the  previous  figure  are  due  to  some  of  the 
cells  having  failed  to  adhere  to  the  capsule.  Photo.  X  264. 

812 


PLATE  3. 


Fig.  7. 

FIGURE  7.  Exp.  70.  Magnetite  arc.  Double  lens  system,  no  screen, 
exposure  20  minutes. 

Lens  capsular  epithelium  2  months  after  exposure,  showing  reparative 
changes.  The  nuclei  vary  greatly  in  size  and  many  of  them  are  extremely 
large.  Some  of  the  cells  contain  double  nuclei.  The  small  dots  in  the  cells 
are  nuclear  buds  constricted  off  from  the  main  nuclei.  They  are  not  related 
in  any  way  to  the  granules  in  Figs.  3  and  4.  Photo.  X  264. 

FIGURE  8.  Magnetite  arc.  Double  lens  system.  Crown  glass  screen  (295 
HIM),  exposure  20  minutes. 

Lens  capsular  epithelium  19  hours  after  exposure,  showing  wall  of  deeply 
staining  cells,  corresponding  in  position  to  the  pupillary  margin.  Photo. 
X  42. 


Fig.  9. 
FIGURE  9.     Exp. 


Fig.  10. 
Single   lens  system,   crown   glass 


54.     Magnetite  arc. 
screen  (295  MM),  exposure  20  minutes. 

Lens  capsular  epithelium  48  hours  after  exposure,  showing  wall.  Many  of 
the  cells  in  the  unexposed  zone  outside  the  wall  are  in  mitosis.  Photo.  X  42. 

FIGURE  10.  Lens  capsular  epithelium  48  hours  after  injection  of  Lugol's 
solution  in  the  anterior  chamber,  showing  wall  similar  to  that  produced  by 
abiotic  radiations.  (See  page  676).  Photo.  X  106. 

813 


PLATE  4. 


Fig.  11. 


Fig.  13. 


Fig.  12. 

FIGURE  11.  Exp.  78.  Magnetite  arc.  Double  lens  system,  water  cell, 
flint  glass  screen  (298  MM),  exposure  1  hour. 

Showing  retinal  ganglion  cells  of  rabbit  unaffected  48  hours  after  exposure. 
Thionin  stain.  Photo.  X  706. 

FIGURE  12.  Exp.  53.  Magnetite  arc.  Single  lens  system,  water  cell, 
crown  glass  screen  (295  MM),  exposure  12  minutes. 

Heat  effect  on  retina  after  48  hours.  In  the  affected  area  the  rods  and  cones 
are  disintegrated  and  the  nuclei  of  the  nuclear  layer  are  fragmented.  The 
inner  layers  of  the  retina  are  normal.  Photo.  X  42. 

FIGURE  13.  Same  experiment.  Affected  portion  of  retina  under  higher 
magnification.  Photo.  X  190. 


Fig.  14. 

FIGURE  14.  Exp.  98.  Sunlight  concentrated  by  large  mirror.  Water  cell, 
no  screen.  Exposure  14  seconds. 

Intense  heat  effect  on  retina  after  six  days.  On  the  left,  the  retina  is  normal. 
On  the  right,  the  outer  layers  including  the  rods  and  cones  are  coagulated  and 
retain  their  forms,  while  the  inner  layers  are  disintegrated,  the  heat  here  having 
been  insufficient  to  coagulate  them.  For  the  same  reason  the  entire  thickness 
of  the  retina  is  disintegrated  at  the  margin  of  the  affected  area.  The  choroid 
shows  a  large  hemorrhagic  extravasation.  Photo.  X  28. 

814 


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3-     .. 


ii  - 

11 


816 


w 


Q  « 


S  S 

a 


817 


I 


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o 


03 

G1 


818 


VOLl'MK 


1.  BELL,  Louis. —  Types  of  Abnormal  Color  Vision,     pp.  1-13.     May,  1914.     35c. 

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May,  1914.     65c. 

3.  PEIRCB,    B.    OSGOOD. —  The    Demagnetizing    Factors    of  Cylindrical    Rods    in 

high,  uniform  Fields,     pp.  51-64.     June,  1914.     -!.">  . 

4.  HALL,   EDWIN   H. —  On   Electric   Conduction   and   Thermoelectric   Action    in 

Metals,     pp.   65-103.     July,    1914.     70c. 

o.  WILSON,  EDWIN  BIDWELL. —  On  the  Theory  of  the  Rectilinear  Oscillator,  pp. 
105-128.  October,  1914.  55c. 

0.  WEBSTER,  DAVID  L. —  Planck's  Radiation  Formula  and  the  Classical  Electro- 
dynamics, pp.  129-145.  January,  1915.  35c. 

7.  PEIRCE,  B.  OSQOOD. —  The  Influence  of  the  Magnetic  Characteristics  of  the 

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Steady  Current  in  the  Primary  Circuit,     pp.  147-168.     January,  1915.     45c. 

8.  BAXTER,  G.  P.,  and  STEWART,  O.  J. —  A  Revision  of  the  Atomic  Weight  of 

Praseodymium.     The   Analysis   of  Praseodymium    Chloride,     pp.    169-195. 
February,  1915.     55c. 

9.  MOORE,  C.  L.  E. —  Geometry  whose  Element  of  Arc  is  a  Linear  Differential 

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222.     June,  1915.     75c. 

10.  REHDER,  ALFRED. —  Synopsis  of  the  Chinese  Species  of  Pyrus.     pp.  223-241. 

June,  1915.     45c. 

11.  DAVIS,    ANDREW    MCFARLAND. —  Certain    old    Chinese    Notes,     pp.    243-2S6. 

June,  1915.     90c.  % 

12.  WHITLOCK,   H.    P. —  A   Critical  Discussion  of  the  Crystal  forms  of  Calcite. 

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